Here's the list: http://store.steampowered.com/search/?specials=1
Included in this list is one of my personal favorites, Crypt of the NecroDancer which has four playable soundtrack remixes.
One of these remixes is currently available at a Name Your Own Price... price. (Which could even be free!)
Synthwave is basically a revival of 80's style synths. It's a lot better than one would think.