I used to use traditional songs for my ringtone's, but i was starting to ruin the songs i would use. Music is a rather big deal to me, so hearing the first 30 seconds of a song i really like everytime i get a call, was starting to take its toll. Took me a little while to listen to "morning bell" by radiohead without having to think of my ringer.
I usually have it on vibrate, because of my work environment. But i use Ennio Morricone's "as a judgement". From the film once upon a time in the west
So you know on Blackberries there's a text message tone called Lightspeed. Well I took that into Garage Band and made it into a loop. That's my ringtone.
Most people think it's annoying but there's something I really like about it.
I use iTunes to create custom ringtones or to convert other format files into m4r format (M4a files with a different extension) for free. The method works on windows as well.