http://www.resexcellence.com/ is the best link for themes etc.
Just make sure you know what your doing when installing themes, it's still really just a hack and if you do it wrong you can make your computer not boot. If you know what your doing, you shouldn't have problems.
As I said in the other topic:
I've had my share of theme caused problems in the past. It's been about a year since my last big problem though because I know what I'm doing now.
Rule 1: only use themes made for the version of OS X you are using (unless you know how to port them)
Rule 2: Keep Aqua Fix installed at all times, and have a printed copy of how to use it from the comand-line (for if things go really wrong).
That's about all there is to it.