Ringtonator Studio allows you to open and edit Quicktime clips, then export them into iTunes’s ringtone format. It works by using QTKit to edit/export the m4a format, and then AtomicParsely to edit the exported song’s metatags so that iTunes recognizes it as a ringtone. It also utilizes the open-source Cocoa add-on SMDoubleSlider. SUPPORTS MP3′S.
To use: check ‘edit manually’ if you wish to crop your ringtone. Drag mp3 from Finder into the Ringtonator. This version only allows for 1 song to be edited at a time (no multiple-file drags for now, doing so will result in only the first file being edited). Edit the opened song to your desire, if you mess up, CMD-R reverts to saved state, while CMD-W closes the song (not the app!). Once you finish, press export. If the original file was not an m4a, it will take a minute to do, just give it some time. Now find the original file again in the finder. There should be a new file next to it called ‘”original file” Ringtone.m4r’. Open iTunes and drag this file in Ringtones menu. Repeat. Read more here

  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!
Your iPhone allows you to assign different ringtones for your different contacts. With iToner, now you can have a Barry White ringtone for when your girlfriend calls, Frank Zappa for when your college buddies ring you up, or the theme from Jaws for when your boss is calling.
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