Utility Belt

Tools of the trade that I've found:

Making CSS faster and better:
CSS Sprite Creator
CSS Optimizer

Page running slow? Yahoo's YSlow integrates into Firebug's Firefox Plugin
Firebug
YSlow
Web Developer's Plugin

Create a sitemap for Google's sitemap submission
XML Sitemaps

This one you have to pay for
Power Mapper

Create a favicon online
Dynamic Drive's Favicon Generator

Post any RSS feed to Twitter
Twitter Feed

Cool Toys from Adobe
Adobe SPRY
Adobe Kuler

Validate your Site for Compliance
W3C
W3C CSS Validator
LitmusApp.com (Premium Services Available)