Arcade: Pac Man and Galaga
Console: Like about ten frillion other people here: Asteroid, Pong, Tanks, etc. on the Atari, the system so ancient John Titor may come back for it some day
(ten points for anyone who gets that reference 
)
Computer: I might have missed it, as I skimmed through the thread to catch up, but I may be the first to mention this: Zork
First graphics-based RPG: Curse of the Azure Bonds (still play it)
First FPS: Marathon (which would explain why I love Halo so much)
First RTS: Civ II
First MMO: Everquest, right after Kunark came out