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Current rotation:

Kill Bill Whistle
Manamana
Cartman Pokerface
The Good The Bad and The Ugly
Gieco

Hehe...
 
The ringtone from the horror movie One Missed Call. The American version; the Japanese version isn't creepy to me.
 
Default: Radiohead, "The National Anthem"
Wife: Smashing Pumpkins, "Thirty-Three"
Parents: Marvin Gaye, intro to "Inner City Blues"
 
I've got different ringtones for different people. For example:

Mum = Purple Rain (her favourite song)
Boyfriend = Baggy Trousers by Madness (all Madness songs remind me of him)

I've got a couple of friends who are in a band and I use one of their songs for their ringtone.
 
Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_0 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A293 Safari/6531.22.7)

Law and Order SVU Theme song
 
When work calls it plays the theme from "Venture Brothers"

My normal ring is the song "Acid Rain" by Liquid Tension Experiment.
 
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