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my default is the mystery zone (spoon). some of my faves customized to contacts are my adidas (run dmc), warbrain (alkaline trio), holding out for a hero (bonnie tyler/flashdance st).
 
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"The Mixed Tape" by Jack's Mannequin!
 
I alternate mine between the theme from The IT Crowd and the elevator-style Imperial March theme from Family Guy: Blue Harvest.
 
My normal ring tone varies, but I've used the following:

Rocky theme
Hawaii Five-O Theme
The Green Hornet Theme
Battle without honor or humanity

My mother in law's ring is the Imperial March, however.

TK
 
I used to use "Old Phone" but made a custom ringtone of the tin can phone ringing from the beginning of the kids show The Wonderpets. My two year old freaks (in a good way) every time the phone rings.
 
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