RogueAmoeba has posted a small Mac application that allows you to copy unprotected AAC files into your iTunes 7.4.1 Ringtones folder. This allows iTunes to sync these ringtones with your iPhone.
The free application appears to simply automate the step-by-step free iTunes Ringtone workaround that has been previously posted.
The application works as advertised and seems to work better than Applegazette's iRing which was an Applescript accomplishing the same task.
This solution, of course, may very well break in the next version of iTunes and only supports unprotected AAC files.