My ringtone is James Blunt's "1973 (Ashley Beedle Remix)." It's a beautiful song and fits the fact that somebody is calling--the lyrics of the ringer go, "I would call you up every Saturday night, and we'd both stay out 'til the morning light, and we sang, 'here we go again.'"
I change mine ALL the time
Most recently it was 'Live Your Life' but the beginning got kinda embarassing
Then it was 'Keeps Gettin' Better' BOW and now it is currently 'Forgive Me'