Far too many to list, but Final Fantasy IX's soundtrack is a tremendous work of art, and a perfect final bow for Nobuo Uematsu from the series. It's always stuck with me among nearly ever other soundtrack.
Notable Mentions (in no order):
- Sonic 2 and 3&K
- Hotline Miami 1 & 2
- Street Fighter 2
- Nier Automata
- Castlevania (Whole Damn Series)
- Donkey Kong Country & 2
- Doom I & II
- Undertale
- Freedom Planet
- Golden Sun 1 & 2
- Hollow Knight
- Skyrim
- Kirby Series
- Mario Series
- MegaMan 2 & 3 (Shout-out to The Megas)
- Super Meat Boy
And so many others, but I'll be here all day if I keep going.