There is now a thread at the official Sims 3 forum which lists links to many fansites with Custom Content.  I urge you to view it for the latest updates.

I’ve been dropping the ball when it comes to posting Sims 3 modding-related news.  A number of sites have already broken the custom-content barrier and are now providing custom clothing, patterns, hair meshes and tweaks to the games (objects are coming, but need more time). Thanks to Sims 3 Nieuws, they’ve directed me to a post by SimGuruHydra containing a few CC links:

Simmers are really quick to find great CC from these sites:
http://www.rosesims2.net/
http://www.peggyzone.com/
http://www.aroundthesims3.com/
http://www.lianasims3.net/
http://www.parsimonious.org/furniture3/
http://www.modthesims.info
http://www.thesimsresource.com/downloads/browse/category/sims3
and many others…!

And for those who are looking for new hair styles, I urge you to check this webpage out.