Wanted to start a thread where all the best music from awesome games can be collected, i'll start the ball rolling with this - "Galvanic Gear" from the Megadrive/Genesis game M.U.S.H.A. (Aleste):
Real composers making real music for a full-length fan game project. Also the sequel just came out and it also has a original soundtrack, but we're waiting for the soundtrack release. It's not retro sounding for the most part but I would say give it a try anyways.
I've heard lots of really good video game music. It's really hard to choose what I think is best. I have played a few games recently that had music by Jake Kaufman, and I think he's very talented. He makes both modern and retro style music. Ultionus (which is basically a Phantis reboot) has some really good retro tunes, and the Bloodrayne Betrayal soundtrack has some nice rockin' gothic tunes that sound a lot like something you would hear in Castlevania (which is a good thing in my case... I love the music in Castlevania). He's done a lot of other good game tunes, too... Shantae, Double Dragon Neon, Mighty Switch Force, etc.
Here is one of my favorites. The funny thing is it doesn't really fit the theme of the ruins at all but it was a really awesome song. I guess it was like a suspense builder as you slowly reached the end of the game.