This site, which has CSS box lessons, is a great resource. Not only does it have a lot of CSS multi-column layout examples, but it also talked about problems and workarounds, and has a rather good rant to read. This site also has a "CSS Panic Guide", some info on text sizing, and even a blog. The blog lists other CSS resources, most of which I have seen, but one I have not.
There is a bunch to check out on this site.
