Which games have the most recognisable/iconic soundtrack/theme?

For me it'd be Tales of Symphonia - play a song from that and I'll know exactly where it's from.

The Elder Scrolls, RollerCoaster Tycoon, Mario, and of course... TRINE/TRINE 2!!! :D
[EDIT] + Bastion. :P

Besides the already mentioned - Braid

Chrono Cross

Plus all mentioned MW2 maybe???

+

Oh Uncharted also....(Beyond TS has agreat one too...)

Blame IWBTG

Half Life 2 is in there also. For me at least :)
Minecraft
Bioshock Series.

Battlefield 2: Modern Combat, i love that main theme

Seriously? You know only 5 "most" iconic soundtracks? I could easily enumerate tens of such. ICO, 999: Nine Hours, Nine Persons, Nine Doors, Baldur's Gate, Unreal, Fahrenheit to name just a few within 10 seconds.

Check out the Final Fantasy music (my favorites are ff VII and XIII), Also loved the music of "The Whispered World" and "The Dark Eye: Chains of Satinav". Oh - and Castlevania: Symphony of the Night is really cool.

Kerbal Space Program has a very distinct and cool Theme song.
Also Metal version and 8-bit :)

Fallout

Ah also a really old game named Bi-nary

Homeworld

It might not be an original score, but GTA: Vice City.

You aren't wrong about Nintendo. Just a couple of bars of the Zelda main game song or the Mario song, and I know instantly where it is from, and I never even owned an SNES/NES. And I'm pretty sure it is the same for most people posting here.