As it turns out, Ambrosia has just released iToner 1.0, their iPhone ringtone tool which we detailed yesterday.
iToner enables you to quickly transfer custom ringtones for your iPhone - without modifying, hacking or having to reset your iPhone. Simply drag and drop your MP3 or AAC audio files on iToner's window, click the Sync button, and you're done! Even better, your ringtones will continue to work with future iPhone OS updates.
The shareware application costs $15 but provides a fully functional demo.