I've got 7 things to recommend. Here we go...
I can't get away from TrackMania 2: Valley. I can't. The whole thing is just good. It's too hard to confidently pick a favorite, but if I had to I'd go with "Vast Veridian."
You also can't go wrong with the Black Mesa soundtrack. "Questionable Ethics 1" is a particularly adrenaline-fueled track.
If you want remixes, the Harmony of Heroes album is not only free but fantastic. I recommend their finale song aptly titled "Harmony of Heroes."
Speaking of Nintendo music, I also think that pretty much anything Kirby is a masterpiece. There's something about the Milky Way Wishes Staff Roll that's too awesome for words, and the acoustic version is just beautiful.
If you want something a bit more chip-tuney, then you can't go wrong with the VVVVVV soundtrack. Especially "Potential for Anything."
All of the BIT.TRIP games have had an emphasis on music, and admittedly I've only played a small selection of them. One of these is BIT.TRIP Presents... Runner 2: Future Legend of Rhythm Alien. Quite the title, and it's got quite the selection. The music is integrated into the game, so you'll notice constants across the soundtrack as a whole, but any given song on its own is still pretty good. I recommend "Superfunk."
Unsurprisingly, I also think that Undertale had an amazing soundtrack. My personal favorite has fluctuated, but I'd currently give it to "Dummy!"
Other honerable mentions include the Bit Blaster XL soundtrack, the whole Hotline Miami series soundtrack, the Frozen Synapse soundtrack, pretty much anything Nintendo, and (of course) the Tower Unite soundtrack.