I almost forgot about this one. An old flash game called "41st Reality". It would be a good game if it's graphic style didn't make it impossible to see what's going on on the screen. But by far the best thing about this game is it's menu music.
Just leave it on the "enter name" screen and enjoy.
http://www.crazymonkeygames.com/41st-Reality.html
edit:
Those are less "obscure" but I think they are deserving of mention:
Someone made a pretty good cover of the Megaman X Storm Eagle stage:
The Doom 3 menu music is also pretty badass:
And so is the Quake 4 menu music:
Hitman Contracts theme song:
