Free Custom Ringtones in iTunes 7.4.1 (Update: Windows Instructions)
1 Rename aac file to .m4r using Get Info (command+I)
2 Double click file to open in itunes
3 Close itunes
4 Goto username/music/itunes/itunes music/ringtones
5 Rename .m4r to .m4a again using Get Info
6 Sync phone
Make sure you name them the way you want, as you cannot remove ringtones (from the iTunes list) once they've been added.
For those having trouble getting this working (and are on a Mac), we recommend iToner.
AppleGazette posted iRing which is a script (for Mac) that will perform the above automatically. Make sure you get the right version (one for iTunes 7.4, another for iTunes 7.4.1)
Update: This post details instructions for how to accomplish this on Windows XP and Vista.

The North Carolina Utilities Commission today officially approved (PDF) Apple's proposal to construct a 4.8-megawatt fuel cell electric generating facility near its data center in Maiden, North...
In the week since Apple's last developer update of OS X Mountain Lion, several new features including hints of automatic app downloads have been discovered in the next-generation operating...
BGR reports that Microsoft is planning to launch Office for iOS in November this year, with the source claiming first-hand knowledge of the software running on an iPad. With the app's splash...
The Palo Alto Online has unearthed plans for a new glass-enclosed retail store going in near the current Stanford mini-store at the Stanford Shopping Center in Palo Alto, CA.
The store will have...