My fave platformers have to be...
Ignore the 3D ones if we're not talking 3D as well!
Ruff'n'Tumble (however loosely it's fits in the genre)
Flashback (Again, awesome but not solely a platformer)
Sonic 2 (The best platform-platformer of all time)
Gunstar Heroes (One of the best games of all time)
Dynamite Headdy (So original, hilarious and downright whacked out)
Sonic (A great incarnation, so different to the MD original)
Mario 64 (The best of the 3D genre, no questions)
Banjo-Kazooie (Great game, lacked the spark that could have made it awesome though)
Rayman 2 (Awesome graphics matched with great levels and puzzles)
Tomb Raider (Despite it's cash cow milkiness, the original was ground breaking and a breathtaking title at the time)
I know I've forgotten some more but I don't want to bore you like I have in other threads