Dragon Warrior NES Famicom Nintendo Sample Demo Cart $1,499.99 Buy It Now for only: $1,499.99

Also:

Intellivision Prototypes On GameGavel
Atari Jaguar test cartridge "Cannon Fodder"
Atari Jaguar Test Cartridge "Theme Park"
Partner64 Nintendo 64 (N64) Development tool
Rareware N64DEV V3 Nintendo 64 (N64) Development tool

Auction Here

Also:

PS3 Uncharted 2: Among Thieves FORTUNE HUNTER Special Edition 1/200
Sega Saturn Black Console (NTSC) - Awesome starter Saturn lot.
DARKHORN: Realm of The Warlords - AVALON HILL APPLE II / Commodore 64 SEALED
Lot 30 NES Nintendo Game Boxes, Boxes Only Lot 2, Lot 3
NES Action Set & MIRACLE PIANO SYSTEM
Limited Edition Fire Emblem Awakening Nintendo 3DS Console Bundle & Artbook
64DD Nintendo 64 Disk Drive Addon
Sega Club Sega Genesis 6 Button Controller - Anyone know more about this? A Sega Club exclusive item I assume.
1994 94 SEGA CHANNEL NOS NEW VINTAGE PATCH
Nintendo Powerfest 94 Competitor Items - Contains the competitor jacket that was given to each of the 132 participants and the competitors plaque.
Metal Gear Rising: Revengeance - High Frequency Plasma Lamp Limited Edition
DUNJONQUEST: 5 APPLE II Games
BioShock Infinite - Murder of Crows - Vigor Replica Bottle - Only 400 bottles were ever made, this is number 153 (carved in on the bottom). This is an exclusive item that was made only for press-demonstrations of BioShock Infinite.
NEC PC Engine Turbo DUO Console System - Nice starter PC Engine lot.
1977 Nintendo COLOR TV GAME 6 Console
Emerald Blue Gamecube Controller - New in Box Japanese Exclusive
Nintendo Gameboy Advance Pokemon Center Gold New York Version
SNES SUPER NINTENDO 24 GAME STORAGE DRAWER CABINET
SG-1000 First Console
1983 Intellivision System Changer - Allows 2600 games to be played on Intellivision.
Atari 2600 The Music Machine
Mad Catz Street Fighter X Sanrio Arcade FightStick
Fallout 3 Wearable Fiberglass Prop Replica Helmet
Pokemon Mini Soft Pocket Monsters
The Walking Dead TellTale Games Clementine Bloody Hat
Game Boy Light Collection 4 Consoles - Tesuka Osamu (Clear red), Astro Boy (Clear), Pokemon Center Tokyo (Yellow), Toys R Us Tokyo (Clear Yellow)
Atari 5200 Prototype Lab Loaner Cartridge - Gremlins
Prototype Atari 5200 SPORT GOOFY
Prototype Atari 5200 LOONEY TUNES HOTEL
Prototype Atari 5200 Realsports Basketball
Prototype Atari 5200 JR. PAC-MAN

Ended:

Sega Sonic the Hedgehog Sega World Sydney Hand Puppet Plush 1997

This setup is the Red/Gray Low Resolution Setup. It can also be seen in a few old Atari videos and displays and was also at some gaming conventions back in the 1990's at the Atari booth.

Since it was in it's Prototype stage and was eventually dropped for the higher resolution Blue/Gray set-up it does have a few minor issues from time to time. Seller has replaced the original ribbon cable connector that connects the Jaguar console to the VR tracker, and includes three new spare connectors. Sometimes the headset shows a double screen, which seller thinks is a minor short. You will need an Atari Jaguar console with hookups and a working controller and also an extra power supply for the tracker The only game released that works with the VR setup is Missile Command 3D which is included boxed and complete. Zone Hunter was rumoured complete but hasn't been found aside from a useless dead Alpine Board long ago. Also included in this lot is a prototype Space Joystick PCB and a Jaguar VR gun and a few other items.

Auction Here

Also:

Atari M*A*S*H MASH 20th Century Fox With T-Shirt
Star Fox BRAND NEW FACTORY SEALED Super Nintendo
Sonic the hedgehog Japan import Super Sonic Sega pin badge
Super mario rpg Super Rare eraser toy set Japan 1996
Nintendo nes Gyromite VGA 85+ gold
Sharp 19SV111 NES Nintendo Television
NIntendo Vintage Super Mario Bros 1989 Plush figure pillow
XBOX - japanese anniversary special edition system SKELETON BLACK
The Jetsons: Cogswell's Caper (Nintendo, 1993) INSTRUCTION MANUAL ONLY
Gun Nac Game for Nintendo Entertainment System - Another game I'm sure I've sold for under $10 multiple times years ago.
Nintendo World Championships 1990 NWC Competition Cartridge Game Repo
Stunt Racer 64 (Nintendo 64, N64) Complete in Box
Nintendo NES game lot 4, 205 games
Nintendo NES game lot 3, 234 tested and working games
Nintendo NES game lot 5, 141 games
New Wizardry: The Return of Werdna -- The Fourth Scenario (Apple IIe/c/c+, 1987)
Sony DTP-H1500 A Development Tool for PSP, QTY 2 PSP DTP-H110 Controllers
Sony Playstation 2 Debugging Console DTL-H30101 Test Console
Sony Playstation 2 Debugging Console DTL-H50002 U Test Console
SONY PSP Developer DTP-H110 Controller Only
Rare Playstation 2 Debugging Station DTL-H50001 Unlocked Multi Region
Nintendo 3DS - Legend Of Zelda 25th Anniversary Limited Edition
RARE M NETWORK ORIGINAL PRESS KIT FOLDER PRICE LIST ATARI 2600 INTELLIVISION
Crash Bandicoot Original Press Kit + Crash Bandicoot 3 Japanese Promo Passport
Nintendo DS Download Station Lot DS NFR
Nintendo DS Download Station with V15 & V17 Demo
Harmony Cart Atari 2600 new
VERY RARE INTELLIVISION LETTER DEALER PRICE LIST CONTROLLER SEVICE FLYER
Cool Donkey Kong Patch
Nintendo 64 (N64) Millennium 2000 Controller
Playstation 2 Original US Linux Kit 2-Disc NTSC
Sharp X68000 Game AKUMAJO DRACULA Castlevania
VINTAGE SUPER NINTENDO SNES SUPER MARIO RPG STORE DISPLAY SIGN VINYL
SONY DTP-T1000A PSP DEVELOPMENT TOOL

Ended:

New The Chalice of Mostania (Coastal Software, Inc., Apple, 5.25")
2002 Legend of ZELDA Burger King Figure
Rental Atari Jaguar Blockbusters IN CASE

This is the real deal, the extremely rare and once thought nonexistent prototypeof the Tengen Version of Tetris which states Licensed by Nintendo on the title screen.

If you are a serious collector and capable of winning this auction,you already know why this cartridge is so rare and so valuable.

Why is this cart so important to video game history?

This important piece of history was followed by one of the ugliest lawsuits in early video game history.
One where Tengen was forced to pull their superior version from the shelves just 4 weeks after release.
Only 100,000 units of the production version of Tengen Tetris were sold during that time period.
Less than a handful of these rare pre-lawsuit prototypes ever existed.

THIS IS A ONE OF A KIND ORIGINAL PROTOTYPE
It is possibly the latest build of Tengen Tetris before the legal action commenced.

The label reads "Tetris Property of TENGEN INC. #4 Prototype:"

The game is housed in a modified Duck Hunt Cartridge. The EPROMs are protected with a thick tape and the cartridge is glued together to prevent piracy and or duplication.

I will NOT attempt to open this cart for pictures of the board for fear it will destroy the prototype altogether. Don't even ask.

Auction Here

One seller has listed a couple cool carts, a demo copy of Mega Man X and another of Super Metroid. Odds are these are final review copies, and the labels look legit. Seller also has a Speedy Gonzales Prototype.

Also:

Donkey Kong Country 3 NSTC SNES Prototype - Cool big board, not cool big price.
Yoshi NES Nintendo Prototype
Nightmare Creatures N64 Prototype
NBA In The Zone 99 N64 Prototype
ToeJam & Earl 2 Prototype Sample Sega Genesis Longboard
Popful Mail Sega CD Beta
Sega Genesis Mortal Kombat 8 Pirate
Sonic 6 (Super Mario Hack) Sega Genesis Pirate
Super Mario Bros World For Sega Megadrive / Genesis
Harry Potter Sega Genesis Pirate
A Bug's Life Sega Genesis Megadrive Pirate
Six Game Loose Virtual Boy Lot
Mario Kart 7 Demo Version - Nintendo 3DS - Not For Resale NFR
Professor Layton and the Curious Village Demo - Nintendo DS - Not For Resale NFR (Euro)
Style Savvy Not For Resale Demo Version NFR Nintendo DS
More Brain Training Demo Version - Nintendo DS - Not For Resale NFR (Euro) - Only $8.00 BIN!
Nintendo NES NTDE 72-60 Pins Cartridge Converter (Lot Of 10, NIB) or a Single Copy
James Buster Douglas Boxing Proto/Sample/EPROM
Nintendo Gamecube DOT-001 Development System Hardware NR Devkit - Pretty decent price at $160. Seller has a scuffed one for $145 as well.
NDEV Nintendo Wii Revolution Development Kit
Lord of the Rings Online Collectors Edition Signed by Developer
Mario Tennis Not For Resale Demo N64
Not for Resale Super Nintendo Ken Griffey Jr.'s Winning Run SNES
Super Mario Bros. Anime Movie Original Soundtack LP
1x Blank Dreamcast HKT-06 GD-R Dev Sega Official NAOMI GD-ROM Katana Development
Devil Course Sample Super Famicom
IS-CGB-EMULATOR Intelligent Systems (CGB Development Emulator)

I posted about a Virus (early Dr. Mario) prototype way back in 2010.

Now, three have popped up on eBay.

From the seller:

This auction is for three (3) different first-party NTSC prototype versions of what would later become the game Dr. Mario for the NES. Each one of these unique cartridges represents a different phase in the development of this title.

Dr. Mario (1990): I bought this cartridge directly from a source in 2008. It was used to take screenshots for the Nintendo Power magazine.

Auction Here - (Super High BIN)

Also:

The legend of Zelda Spirit Tracks limited edition nintendo DS sealed steelbook
Zelda Collection Club Nintendo Gamecube Japan
BIT60 The Real Atari 2600 Computer System CIB
Original 1980's Atari Retail Spinning Display Case
Dark Sypro Skylanders Figure
NES Flintstones 2 The Surprise at Dinosaur Peak - PAL B Version
11 NFR Nintendo DS & 3DS Demo Cart Lot
NES M82
NES German Lion King
SUPER ADVENTURE QUESTS NES (Codemasters)
German NES Pinball

This is pretty cool. It was a review copy sent to EGM directly from Tengen. It's a prototype of the Tengen Version of Tetris which states Licensed by Nintendo on the title screen.

The label reads "Tetris Property of TENGEN INC. #4 Prototype:". It's housed in a modified Duck Hunt Cartridge. The EPROMs are protected with a thick tape and the cartridge is glued together to prevent piracy and or duplication.

Auction Here

For history on the Tengen Vs. Nintendo issues, check here.

Also:

Loose GBA Ninja Five-O
Earthworm Jim 2 Sega Genesis Prototype - Seller says there are differences.
Data Age Frankenstein's Monster Demo Proto Game Cartridge Atari 2600
Mega Man X Super Nintendo NTSC Demo Final ROM Version - Production board, so more like a review copy.
Killer Instinct (Nintendo) E3 1995 Tradeshow Pin
Nintendo Power Issue 1 July/August 1988 Sealed in Mailer - This is the original mailer which contains issue 1 of Nintendo Power and all the subscription information inside. The contents have never been touched by human hands as the envelope is still intact and never been opened.
SNES Promo Store Display Sign Promotional Vegas Stakes
N64 Store Display Button Pin SummerBlast Nintendo 64
Earthworm Jim 1 & 2 Store Display Box
N64 Store Display Button Pin Funtastic Nintendo 64
Nintendo Power Store Display Promo Promotional Nester Sign
Gameboy Tetris Store Display Nintendo Sign
SNES 3D Store Display Button Pin
Super Mario Bros. 2 NES Store Display Standee Promo
VINTAGE NINTENDO SNES WISDOM TREE GAME SUPER NOAH ARK 3D UNCIRCULATED ROLL
VINTAGE NINTENDO NES WISDOM TREE BIBLE BUFFET UNCIRCULATED GAME STICKER ROLL
VINTAGE NINTENDO NES WISDOM TREE BIBLE ADVENTURES UNCIRCULATED GAME STICKER ROLL
Jak And Daxter Precursor Legacy Press Kit Shirt Promotion - Only $1.00.
NEW KIDS ON THE BLOCK - NINTENDO NES MOCK-UP / PRE-PRODUCTION BOX ART - Sold awhile back for roughly $300. Now, a mere $249,999.99.
Vice Project Doom NINTENDO NES SAMPLE/DEMO + MOCK BOX & INSTRUCTIONS - Cheap in comparison. Only $74,999.99.
Brand New Unplayed Boxed Sega Master System Black Console (PAL)
God of War Skateboard Deck
Sega Game Gear Light Blue Limited Ninku Edition New Boxed Complete
Grand Theft Auto IV Graphite pool cue
Factory-boxed Brand New Super Nintendo (SNES) PAL consoles - Seller seems to have a bunch.
POKEMON LEGENDARY DOGS DISTRIBUTION CART
Official DRAW TIE EMPLOYEE ONLY Atari Jaguar Collector's Badge - According to seller these were worn by employees at the release of the Jaguar system.
Super Nintendo (snes) Game - Super Metroid - Big Box - Pal

Ended:

Nintendo M82 Store Display Demo Kiosk with Full Size Arcade-style Cabinet - Mentioned this already, but it sold for a cool $4,550.00.