It comes with only slight hesitation at choosing my favorite video game tune. That would be "The Opened Way" from Shadow of the Colossus. Nothing better captures that feeling of an encounter with a colossus. Even without playing the game, I could visualize taking down a giant to this song! It is unfortunate the composer, Kow Otani, rarely does music for games but with the SoTC soundtrack it's clear he has still left a huge mark on gaming.
There’s lots of great video game tunes out there (most of the Final
Fantasy soundtracks spring to mind) but none have the lasting power of
this one to me. Even the best songs, from video games or elsewhere, get
tiring after listening to them 40 or 50 times. For some reason, this one
is an exception.
Everyone has their own favorite though, so go ahead and share yours (or at least the first one you can think of)!