I use just a generic, ordinary ring. I am not a big fan of ring tones, and never have been.
I have a couple of points about ringtones: Obscene ring tones are not cool, and I find them quite obnoxious. When I am standing in line for the movies, or what have you with my kids, it's really pretty sad when some parent's cell phone goes off, and plays some obscene rap song ring-tone.... great example to set for the kids, and a real classy move to boot.
I love the idiot in the restaurant fast food joint the other day.... his phone goes off, making x-rated sound effects... and he wasn't even embarrassed.... He answers his phone, with a "hey dude" followed by a couple of "F" bombs... It was a classy moment...