One of my favorite bonuses for games are soundtracks so I'd like to hear what some of your favorite soundtracks are. Soundtracks that are available with purchase of the game on GOG please.

From what I've heard I would have to go with the Planescape Torment soundtrack as my favorite so far.

@Ric1987
If you like music from PT you should go for Fallout and DeusEx - same composer.

That reminds me I need to purchase the Fallouts on here at some point. Fallout Trilogy doesn't work too well for me which of I course I bought only a few weeks before finding out about GOG.

Total Annihilation, Heroes of M&M 2 and 3.
Those are the best, IMO.

Deus Ex, Fallout (especially Fallout: Remastered soundtrack's great, google), PS:T, beyond good and evil's fine, The Longest Journey...

I really like the Planescape Torment OST, it really transports the morbid mood of PST...
And Evil Genius! It's awesome! God, I love Evil Genius.

I agree with all of klaymen's suggestions, and also, Evil Genius, but also add Stronghold and Stronghold Crusader. Those have very immersive and great-sounding soundtracks.

Total Annihilation has one of the best soundtracks ever really enhances the game mood.

I also Like Baulders Gate music as well it can feel epic at times.

Prince of Persia: The Sands of Time.

Maybe I won't be the only one unique snowflake here, but Heroes of Might and Magic 3. There is something in those tunes that calls in my head visions of brave knights and epic castles and dragons above the meadows ;)

Total Annihilation

Outcast.

It's funny that, on the other hand, I say HoMM 3's soundtrack is the least "epic" of all five (OK, still above 1). It's great among game soundtracks on its own, but I feel it's much more... distant than other HoMM soundtracks.

Thunderscape. OH WAIT.

I really like the Sands of Time soundtrack.

Blood, try Fate of the Damned.

+1 to Total Annihilation too.