Super Mario Bros. 3
Super Mario World
Sonic the Hedgehog 1/2/3/& Knuckles
Street Fighter II (arcade)
Tony Hawk's Pro Skater (on N64)
Tony Hawk's Pro Skater 2 (on PC)
Goldeneye 64 (I'd weep with shame to know just how many hours I've blown on that wretched game)
Mutant League Football - the only truly worthwhile football game
Half-Life 2 (Steam only counts 52 hours, but I know I've passed 100 if you count the hours from before Steam kept track)
Legend of Zelda: OoT
Super Mario 64
maybe NFL Blitz
probably all three Halos, sadly
Fortunately for my pride, none of those were multiplayer (except the Halo games, and even then not online).
Also, it seems a bit cheap to count the likes of the Sonic games, SMB3, and SMW, since I've been playing those off and on for much of my life. Really, if we're counting 100 hours around the time I bought said game, I'd say Goldeneye, the first two Tony Hawks, and Half-Life 2.