For a good HTML/CSS reference I would recommend
W3Schools
Even if you already know what you are doing, the tag/attribute lookup tables are very handy if you know what you want, but cant remember it exactly.
Plus it has a 'Try-out' section where you can type code in one frame, click a button and have it appear in a frame next to the code. Very handy for quickly testing Javascript or CSS.
If you're serious about making a decent (dynamic) page then I also recommend learning PHP and SQL (specifically MySQL)
Get Apache 2, PHP 4 and MySQL 2.23 (plus the relevant online/dowloadable Manuals) and set up a localhost on your own pc and start playing about.
You can make some complex looking dynamic pages with very simple code.
Of course then theres not just PHP, theres Perl, ASP, and JSP to name a few. And theres just as many other free SQL and HTTP servers as well, go with whatever suits you best.