I have to agree with Joel about the Robocop 3 theme on the Commodore 64. The Nes version of Robocop 3 has a very similar tune although the bassline is a bit different. Actually the Spectrum version half-heartedly tries the same tune but its pretty weak.
I think the WiiWare music for Cave Story isn't very good. I'm still blown away with Cave Story and now I've realised how cool the music is too. Did he make everything in the game by himself?
Same with The Underside. It has really great music too.