smashTheTONES is a really cool site where you can upload your own images or ringtones to your phone. I was a little skeptical at first about entering my cell phone number at a website I'd never heard of, but a small amount of research shows that it's been featured in publications and on news programs, and is quite legitimate.
I've just been experimenting with my own polyphonic ringtones (ie, MIDI files), and I've made some MP3s of the ones I put together this evening. They're mostly taken from pieces of music I'd written some time ago, which I've had to edit down to no more than four MIDI voices plus percussion (is that standard? It's what my phone requires). The bass didn't come through very well in the recordings, but I'm terribly thrilled with the ringtones nonetheless. The files are small (all in the ballpark of 200K), so check 'em out:
In retrospect, I could so totally have composed Nintendo soundtracks, circa 1987.