www.alistapart.com
www.w3.org
www.glish.com/css/
Install copies of Mozilla (
www.mozilla.org) and Opera (
www.opera.com) so you can check how your pages look in other more standards compliant browsers.
One technique I (and many others) use is to save copies of pages on my hard disk so I can then look at the code to see how it was put together. I find Opera's 'Save with images as...' works best for this.