I used to use Onyx, Font finagler, and a few others but i just stopped.
I learned good methods of organizing my files, fonts and using disk utility to repair permissions and clenaing out browser caches.
that seems to do just fine fo rme now, i just dont like the idea of a 3rd party program touching system files and reorganizing them for me,
though im not totally against a nice cleaning utility, Onyx is a good free all in one type of solution though.