There's nothing like Jamendo right now.
I think the easiest and best thing to do right now is to make them on your Mac or PC, using Audacity, Sound Studio, Garageband, etc, so that you can add in fades and other niceties, and then save them, convert them (if necessary) to AAC, and rename them with .m4r filenames. Then, as long as they are < 0:30 long, you can re-import them into iTunes and they will add in as ringtones.
The big benefit of this over Jamendo is that, when you made ringtones on Jamendo, they didn't survive whenever you updated the iPhone, even if you restored from backup. Ones in iTunes do.