I have a few rare PS1 and PS2 games, but untimately, I haven't been collecting long enough to have a big-bucks game. I have an Atlus game, those are always going to be rare, and I have a few jap-to-US games that sell pretty high here because of how they were marketed (Bundle packs). But honestly, I don't see why a game needs to be rare. Atlus ALWAYS makes their games limited thanks to their marketing campaign and releasing as few in the series as possible, but a game is simply data encoded on a disc. You would figure that the game companies would release a great number of a game and make more money.
AND I CAN'T FIND ICO ANYWHERE FOR A GOOD PRICE! DARN YOU RARE RELEASES!