My current dupes:

NES:
Final Fantasy
Legend of Zelda 2, The: The Adventure of Link
Mighty Final Fight
Yo! Noid

SNES:
Super Star Wars
Super Star Wars: Return of the Jedi
WWF Super Wrestlemania

Genesis:
Sonic 3D Blast

There is a long list of games I'm interested in, and (yes) I know what they're worth and would be willing to trade +$.

Some of the highlights include:

NES:
Bucky O'Hare
Gargoyles Quest II
Vice: Project Doom
Jackie Chan Action Kung-Fu
Uninvited
Trog
8 Eyes
Menace Beach
Wacky Races
Gemfire
Krion Conquest
Felix the Cat

SNES:
EVO
Earthbound
Megaman 7
Mega Man X3
Wild Guns
Super Bonk
Skyblazer
Ogre Battle
Spiderman: Maximum Carnage (*red cart*)
Metal Warriors
Captain Commando
Hagane
Ghoul Patrol
Biker Mice from Mars
Knights of the Round
Magic Sword
Run Sabre
King of Dragons

Genesis:
A number of games, including all Shining Force games, Sparkster, Yu Yu Hakusho, Steel Empire, and Shadowrun.

Not them, but I've ordered games from both Flashback entertainment and Gamereproductions.com. I've been very happy with both orders!

Yeah, but it's online only and their prices are so-so. If possible, I recommend finding out if there's a non-chain store in your area that deals in retro stuff and giving them your business. I've been a pretty regular customer at mine, and made friends with some of the staff, and they keep an eye out for stuff I'm looking for and give me a call if something interesting comes in.

No offense if any pinsiders work at Gamestop, but I avoid that store like the plague. Too many aggressive and predatory sales tactics. It's often like walking into a Games Workshop store, if any of you are tabletop geeks as well.

I see a few copies on eBay for $40 cartridge only (there's one $40 in box, but the cart itself is in TERRIBLE shape. Still plays, supposedly, though).

I was lucky enough to find mine in the wild a few years back in a box some old lady brought up from the basement for a garage sale. Haven't seen one since, though.

I have one! While I still pull out my original hardware from time to time, in terms of cord management alone, this thing is awesome. And, it has an hdmi output and essentially acts as a framemeister so your games look amazing on a modern TV.

Cons: the packaged controller is awful. Luckily, there are inputs on the side for NES, SNES, and Genesis controllers, so it's not a huge deal.

The other problem is that since this thing essentially downloads the cart ROM and plays it from it's own hardware, you have to remember to upload your save game data back to the cart, otherwise it won't be there when you plug the cart into a regular console.

All that aside, I still highly recommend the Retron for anyone with a large cartridge collection.