Well, I like all the classics like early Megaman, Nobuo Uematsu, Yasunori Mitsuda, Hitoshi Sakimoto, anything from Falcom (Y's, Xanadu, etc).
There are some truly oddball compositions out there that are dear to me, like a lot of the work of Zuntata, which was an in-house band for Taito in the 90's. Similarly, a lot of the weird, sample-based music from the Amiga-era, from people like Chris Huelsbeck, Dave Wittaker and Rob Hubbard.
In recent years, from Japan I've really gotten into anything that Yoko Shimomura has done, and Michiru Yamane upended/revitalized some of the later Castlevania's music in the best way possible.
I will always go to Koichi Sugiyama's Dragon Quest music whenever I want to turn someone on to truly beautiful game compositions (chills), or just relax. Also Matt Uelmen's music for Diablo 2 and Torchlight games also veers toward more contemporary genre's, but is atmospheric, masterful and provides a really well-done alternative sound for what we usually get in interactive media.
Some super strange stuff that just sticks out as not belonging anywhere else: Katamari Damacy's OST, the VibRibbon soundtrack, the Neverhood soundtrack by Terry Taylor, the hidden gem that is the "Moon: Remix RPG Adventure" soundtrack (seriously a great one; check it out).
I have a lot of game music and it's my primary soundtrack while I work.

How did Matt Uelmen ever come up with this in the first place... what a stroke of genius.

I want Matt Uelmen back, but this is good as well. The music certainly has scaled up from the older games.