My first phone had a shitty MIDI version of Slayer's South of Heaven (if I remember right, it just used the intro). Then, when I moved on to a better phone that could play MP3's, I switched to the theme from Metalocalypse, which is probably the best alarm I've ever had, other than that one morning I accidentally had my Ipod on Merzbow.

On my new phone, I just have the standard ring on, because I've been too lazy to make myself a ringtone. When I get around to doing it, it will probably be some part of Freezepop's Parlez-vous Freezepop? (Inter:sect remix) because that song is fantastic.