Rings Extended?

I use it and I like it b/c it makes finding your music files easier (when assigning a ring).

If you like that, you might want to try Ringdroid which will allow you to take clips of songs and use them as ringtones (if you want a specific portion of a song)

Just go to the built in music app. Play any MP3 song, and while it's playing, press the Menu key and select use as ringtone. It doesn't let you select just part of a song, but there are tons of free apps (I have a Mac so I just use quicktime) that will let you trim an MP3.