As a webmaster, especially if you are a solo webmaster, it's hard to keep all the moving parts of the web in your head at once, let alone the detailed syntax of every HTML attribute and configuration option. It's vital to have the right references at your fingertips to get those details fast. These are eight references every webmaster should have on their quick bookmarks list.
- HTML 4.01 Specification - Because the XHTML spec says "just like HTML 4 except..."
- XHTML 1.0 (Second Edition) - Describes the differences between HTML 4 and XHTML.
- Cascading Style Sheets, level 2 revision 1 - The CSS Specification.
- HTTP/1.1 (RFC2616) - The HTTP spec, useful as a quick reference to HTTP status codes and official headers.
- JavaScript - Mozilla Development Center - Probably the best one-stop for Javascript references, including the DOM and a collection of articles on AJAX and DHTML.
- MySQL 5.0 Reference Manual - If you are building server-side applications, chances are very good you are using MySQL, in which case you will refer to this often.
- Internet Explorer Developer Center - If you build web front-ends, you probably spend a huge chunk of your time tweaking around the differences in various browsers. Hopefully Microsoft's docs on IE can help smooth things out.
- Apache HTTP Server Documentaton - Because you need it.

