Another set of tools that I don't know how I was living without before:
Firebug integrates with
Firefox to put a wealth of web development tools at your fingertips while you
browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any
web page.
http://www.getfirebug.com/
YSlow for Firebug
http://developer.yahoo.com/yslow/
