I am taking a CSS course, and I love it! Amazing how you can do so many things with it. I remember someone here (I think it was Smyrl) posting a page where all the CSS commands were posted, and it also had some examples, does anyone remember that page?
A great example of the possibilities of CSS is http://www.csszengarden.com and then theres also http://www.stylegala.com which is a pretty good resource for inspiration. Beware crossbrowser differences though. There's always a catch anytime you are doing something even remotely complicated. Another great tool is the webdevelopers plugin for firefox - you can edit stylesheets in the browser and see the results immediately. He also has a user agent switcher plugin that's helpful when you want to see what a site is showing various user agents. It only comes with a few out of the box, but you can add your own or there's a giant list out there that I downloaded but I'm not sure from where.
I like this one: http://www.w3schools.com/css/css_examples.asp Clicking on the links, it brings up the Tryit Editor, which allows you to change stuff and see what it actually does. 'Classification' and 'Positioning' sections were particularly helpful.
They have to pay for the bandwidth somehow... and I know I ate up alot. Besides, she says whatever you want her to...
The CSS Zen Garden is a good site. You should also check out the associated book, which is a fun read and helped my design skills as well as giving me some hints on CSS. I would recommend a book rather than a website for your CSS reference; especially if you've taken a course so really what you want is just an aide memoire. Try CSS Pocket Reference (no affiliate stuff, don't worry!). I use this book every day, don't think it's ever actually made it to my bookshelf.