Bwahaha If we're talking Pure OSTs I have way, way too many! XD
Loads from Indie bundles alone!
But I also have over 200 GOG titles, many of which include a soundtrack as well!
I will admit I like the Descent Soundtrack, some of the tunes off Might and Magic, and I love almost every indie chiptune I hear.
(Once I get my 2 32gb Class 10 microSDs and my second memory card adapter for my PSP I'm going to add loads more music to my old card (planning to split my games and music into two 64gb cards you see (a 128gb PSP is a beastly concept!

)). I'd have 64gb to play with, and thats A LOT of music)
(I'm into chiptunes at the moment. Virt and Disasterpeace are amongst the best at their craft. Preschtale by C-Jeff is just fantastic. Taking the concept to a whole new level!)
EDIT: Oh and Castlevania.
I'm really liking Castlevania's music again. Enough for me to go back to the games and play them on the Wii.
(Emulating NES on Wii and playing with the Wiimote is very comfortable. I recommend it!

)
I'm also unashamably admitting that I practically know Megaman 2's music off by heart! HAHA!