I recently attended a talk by a web developer who is involved with the CSS Discuss list. They have a wiki at css-discuss. The wiki is notable for two reasons. First, it is a very full set of discussions on topics of interest in CSS. Second, from what I have been able to learn, this list has an outstanding membership, and the big guns in CSS are involved here. So the site should be a great resource for everything to do with CSS.
The home page for css-discuss. org is, not surprisingly, http://www.css-discuss.org/.