Happy Birthday! Here are your souls
Aquaria OST:
https://infiniteammo.bandcamp.com/album/aquaria-original-soundtrack
They all are pretty great. My favorite song is "Remains". Also I like "Light", "Moment", "Lost Waters", "Title", "Icy Waters", "Undiscovered Waters", "The Return", "The Traveller".
"Fear the Dark" is best one in the list, but it has words.
Game is good, too.
To the Moon OST:
I highly recommend playing the game before listening to the songs, as they create half of the game. Atmosphere is everything. Game is not very long btw. Also turn off your phone and prepare to play it in one sitting.
You can listen to the Main Theme, since it plays in main menu.
https://freebirdgames.bandcamp.com/album/to-the-moon-ost
"Moongazer", "Born a Stranger", "Anya by Stars", "Main Theme", "For River", "Once Upon a Memory", "Tomorrow", "Lament of a Stranger".
Braid OST:
http://braid-game.com/news/2009/04/braid-soundtrack-album-now-available-with-new-songs/
Probably "Tell It By Heart" and "Romanesca" are my favorites.
Knytt Stories OST:
Game is free, music is .ogg format.
http://nifflas.ni2.se/?page=Knytt+Stories
Check the tracks here:
Cave Story OST:
Original is free, remake with better graphics is available to buy on Steam.
http://www.cavestory.org/download/music.php
Favorites: "On to Grasstown", "Moonsong", "Access", "Cave Story" (main theme), "Labyrinth Fight", "Mischievous Robot".
One Way Heroics OST:
Game is available on Steam. No official OST is released. Soundtrack can partly be found here: http://windsphere.biz/a_music_mp3.shtml
or here: http://steamcommunity.com/app/266210/discussions/0/540739405754809884/
or on utube:
Favorite track is "ugly cygnet \ quiet" by windsphere.
Pixel Piracy OST:
https://koleaudiosolutions.bandcamp.com/album/pixel-piracy-original-soundtrack
Those songs are hilarious. They have words in them, but they are actually in the game.
"My Favorite Things Start with a 'P'", "9 Drinks", "Salty Dogs"
Shadowman has nice OST, but I think you already know it, since you used one of the songs in "The Tunnel".
Arcanum has some of the best tracks, but its a popular game.
JetsNGuns has awesome tracks too.
