Using Mozilla in testing and debugging web sites
A guide to all the tools Mozilla makes available for debugging websites, especially useful for debugging web applications and complicated JavaScript code. From the DOM inspector to JavaScript debugger, you’ll probably find something you didn’t know existed.

bbPress
Forum software from the makers of WordPress. Having explored the code base a bit when writing my first plugin, I can say these guys practice good coding standards, and extending their stuff is straightforward. A whole different world from the hole-riddled mess called phpBB most sites use. Thanks Brendon for the link.

Amberjack
Another site pointed out by Brendon, Amberjack lets you create website “tours” with just JavaScript. It overlays information about webpages over the actual webpage along with navigation buttons to move page to page. A good way to show off features of a web service or product you’re trying to sell.

The Web Developer’s List of Resources
While not the most visually appealing site, I found a couple useful sites from the list, which is editable by the site users by “pinning” or “unpinning” links you like or don’t like.

iWebTools
A collection of extremely useful tools for search engine optimization. I always use their PageRank checker when an update is going on since it checks two dozen different servers at the same time.