The Kakophone is an online ringtone generator for your cell phone (mobile phone, for the rest of the world).
Generating your own music is quite simple: just a few clicks (of mysterious buttons, although I suspect you'll get the hang of it if you spend some time there).
You can then download (MIDI format) or have the resulting ringtone sent to your phone. Corrected Link - via Ursi's Blog
My ringtone is:
http://www.kakophone.com/wap2/5999/Funcurre.mid