most memorable soundtrack you ever heard in a game

Based on how well it fits the theme, it's a tie between Silent Hill and Hotline Miami. Deus Ex and Unreal Tournament are close third and fourth.

Bastion, Hotline Miami, GTA series (SA at most) - this is just great music that you should listen out of the game
also To the Moon main theme is very memorable

Either Austin Wintory's soundtrack to Journey or Gustavo Santaolalla's work on The Last Of Us

Most memorable soundtrack : Melodies of Life from FF9

Mafia: The City of Lost Heaven (2002) - Soundtrack

View attached image.

https://www.youtube.com/watch?v=5XR3ckkbxzc

Shatter
http://sidhe.bandcamp.com/album/shatter-official-videogame-soundtrack

I almost bought it twice by accident

DmC: Devil May Cry
Noisia - Mundus Theme

https://www.youtube.com/watch?v=FP4ldBkQvw4#t=52

To the Moon: https://www.youtube.com/watch?v=LsAsJUTsYxs

Ragnarok Online & Pokemon...

portal 1 ending

"this was a triumph"

https://www.youtube.com/watch?v=Y6ljFaKRTrI

Diablo, i can easily guess Tristram theme even if you wake me up midnight after getting drunk

chrono trigger - secret of the forest

Guild Wars

Chrono Trigger

Two years since, and still this song comes up from time to time

https://www.youtube.com/watch?v=7M1k1tgq87g - Children of the Elder God

mass effect 3

Song of Storms

Just played Jet Set Radio on Steam and the soundtrack takes me back to the Dreamcast days. :D All techno/underground hip-hop like.

I am pretty sure that it might be Mass Effect (first one) credits song, M4 Part II by Faunts.

After ending of the game I just was sitting still with my eyes wide open and feeling story with all my senses.

But Witcher 3 have a chance to change here sth :). Check Percival Shuttenbach on youtube.

Another vote for "To the Moon".

Bastion.

Bastion, Transistor, Metal Gear Rising Revengance, and DMC 1-4.

Definitely Planescape: Torment. Though Mark Morgan's work on Wasteland 2 isn't to be sneezed at either, and the samples for Torment: Tides of Numenera also sound promising.

But Planescape: Torment... especially Deionarra's Theme and Fortress of Regrets...

Archeage "fertile plains" look it up.