My favorite soundtrack ever, of course, is that of The Secret of Monkey Island (MT-32) by Michael Land. A lot of nostalgia there.
I also very much like the soundtrack to Dune by Stephane Picq. There's an edition that combines the Adlib, Adlib Gold, and MT-32 versions which is "chef's kiss". Alternatively, I can recommend the Space Opera edition.
Strike Commander by Nenad Vugrinec on MT-32 is also great.
For chiptunes, I really liked Penny Arcade's On the Rain-Slick Precipice of Darkness 3 by Alex Mauer.
Or, for a real classic, Earthbound by Keiichi Suzuki and Hirokazu Tanaka.
Yes, I have a bit of a thing for retro sounds. ๐