I do enjoy the Halo theme quite a bit, but it's not my favorite.  Some other good orchestral stuff:

FFIX

My 2 favorite Zelda songs:

Try Live and Learn from Sonic Adventure 2. Theme song from an awesome game. Rocks.

http://www.youtube.com/watch?v=kZLplLJOf1w

That's how you get me hooked on a game. Awesome rock music.

Of course I have to post at least a couple songs from one of my favorite franchises ever.  Enjoy the wonderous melodies of Gyakuten Meets Orchestra!

Ace Attorney 3

Ace Attorney 4

@naznatips: The ones you showed were good however I did not find any exceptional. I remember there was 1 song from Ace Attorney that was amazing (an orchestrated version), but wouldn't be able to find it though.

Some exceptional Classical music:

Crysis - First Light:

Mafia - Main Theme:

Deus Ex - Main Theme (Orchestral version): This game is so f*****g Epic

I think Final Fantasy VIII has the best video game music ever. I pretty much love every single musical piece in it. Love it to bits. It really does bring back the memories.

Final Fantasy 6 PWNS all other soundtracks

Terra's theme



Opera scene




Searching for Friends




& the MGS Main Theme

@Soriku

I guess you havn't played FF6 then.

Meh, I couldn't say which would be the single greatest piece of video game music ever, but I've always found the music in the Zelda games to be the most awesome.

Various Zelda and Final Fantasy music and SotC

I like my xenogears music most.