This site is yet another CSS reference site; but I like it because it is almost like having CSS flash cards; the information is short and sweet. However, I do find the ads annoying (too much animation) and the text renders really strangely in my browser, like it's blurred or something.
I think this is useful! It took me a minute to figure out I was on Chapter 4 (I'd like the chapter selected to show it is selected ), but the examples of the usage of the CSS is well worth a little bit of confusion.