Every handheld Kingdom Hearts game (Especially Chain of Memories for the GBA)There's something about taking the Keyblade on the go that makes me all nostalgic inside... especially since Chain of Memories was my first Kingdom Hearts game...
Rayman 3It's not the first Rayman game I've played, but it was the first one I beaten to full completion... *sighs* Good times...
Game and Watch Gallery 4Mario vs Donkey Kong in a haunted mansion... Mario and Luigi packing pastries with Bowser... Shit got intense to the point of nostalgia...
Jak 2Needed a GTA replacement... This was the game that had to do it for me before The Simpsons Hit & Run took cared of that... At least it introduced me to a trilogy in the making, basically...
The Simpsons Hit & RunMy one, true GTA-based nostalgia... Also, them seasonal references as well as them cheat codes...
Metroid Prime/PortalBasically, both games made me rethink my stance on First-Person-based games...
RezCame for the shooting... Stayed for the soundtrack... Nostalgia for all of the above, which all lead to Child of Eden...
Pokemon (In general)Dabbed in the first two generations, played through the third, skipped the fourth (due to lack of a DS at the time), played through the fifth and sixth, and REALLY wants another Pokemon Pinball game right about now...
Those are just off the top of my head, mind you...