The following are MIDI files suitable for use as polyphonic ringtones. I did not sequence these myself, nor do I know who did so. As far as I know, all of these files are in the public domain.

Hip-Hop
Freak Nasty - Da Dip
50 Cent - Patiently Waiting
Dr. Dre - Still Dre
Eminem - I am
Eminem - Superman
Gorillaz - 19-2000
Outkast - So Fresh So Clean
Cypress Hill - Rock Superstar

Rock
Metallica - Enter Sandman
Led Zepplin - Stairway to Heaven

Video Game/Other
Mike Tyson's Punch-Out
A simple drum roll
Theme from Monty Python & The Holy Grail
Music from De Beers commercial