Definitely everything from Konami (or UltraGames at the time). It's too hard to pick one definitive ''best'' soundtrack.
I especially enjoy musics from Gradius, Gradius II, Salamander, TMNT 2: The Arcade Edition, TMNT 3: The Manhattan Project, Castlevania, Contra, Super C and Top Gun: The Second Attack. Classics!
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...