I use iTunes and Audacity to make mine. I've modified the process in the link below to best suit my needs/wants. Basically, I use Audacity to crop, fade, and adjust the gain (so it's not staticy), then import that file into iTunes. Inside iTunes, I convert the file to AAC, drag it to my desktop, change the extension to M4R and doubleclick to add it to the iTunes ringtones.
You can do most of this from directly inside iTunes, but I find it easier to edit the file in Audacity.