iToner. iToner from Ambrosia Software allows you to move almost any sound file to your iPhone as a custom ringtone.
- Almost any sound file. MP3, AAC, WAVE, or AIFF
- Drag and drop interface.
- Free trial.
- Low cost ~ $15.00.
- No need to purchase the song and then the ringtone from iTunes.
- No jailbreak required.
Doesn't work with purchased iTunes songs though. Fair enough.
Oh And it's Mac OS only.
Still a win-win.