Bubble Bobble Part 2, nes only available at blockbuster video near the end of the nes life
Bonk's Adventure NES
Bonk 3, bonk's big adventure tg-16
Solitaire nes
Aero the Acrobat 2 and Aerobiz super sonic for genesis
Pole Posistion, Diner, and Dig Dug for intellivision
Miracle Piano for nes
Odyssey Shooting Gallery (absolutely awesome)
Death Trap 2600
Sector Alpha and Spectron for colecovision
Chavez 2 (ludicrously rare, but no one cares) Ardy Lightfoot , and ughh, bebe's kids (worst game ever, seriously) for snes
and Sengoku 3 for the NEo geo (only 500 were made to begin with and many have been sac'ed to make conversion carts)
the best part is outside of Sengoku 3, I didn't pay more than $10 for any of them
I also used to have some really rare virtual demo carts of Red ALarm Wario land and and late release US master system games like Golden Axe Warrior and Sonic the Hedgehog, but I sold them as I like money more than upc stickers and not for resale labels, seriously my US copy of Sonic the Hedgehog sms went for 200 dollars a few years ago, I then imported a British copy for an entire 10 dollars

Is Ico really rare? Some online stores still have it in stock and you can get it for like 20-25€ on ebay.

phantasy star 1 for master system, with box and instructions

It's got to be Metal Gear Solid: Special Missions I suppose. Well, it's not that rare in the end... But it's definitely not too common either.

I agree with Son1x about ICO here. I got it a year or so ago and it was pretty cheap. There were other people selling it, too. Did I mention my copy was apparently a re-release or something as well? It even had a Shadow of the Colossus ad on the back of its manual.

Goldeneye 007
Perfect Dark
Donkery Kong 64
Banjo Kazooie
Banjo Tooie
Donkey Kong Country (1, 2 and 3)

Oh yea, Ico had a re-release in Europe(PAL actualy). I just remembered.

Hmm.. I guess some of my older PC games are kinda rare. I have X-Com 1-3, King of Dragon Pass, The Dig, Sam & Max: Hit the Road, Wing Commander 2, Ultima VIII, and a bunch of other ancient stuff on CD.

The PS2 version of Rez....

And Steel Battalion, my pride and joy.

Pretty much nothing except Rez (PS2). I looked through all my old PC games are they're all pretty common.

Tetris 2 for the NES
Zombies ate my neighbors SNES
Metroid 2 Return of Samus Gameboy