Are you a web admin? If so, check out Netcraft's set of web server and network interrogation tools.

Not sure what to log for that support request resolution? You need to get down with the lingo.

Nadav Savio of Antenna fame has written a typography tutorial for WebMonkey, or as he puts it, a "mini-guidebook to the strange and magical land of type".

Into XML? Check out this fairly comprehensive list of XML tools.

Adaptive Path has made a representative sample of its user experience presentations (and associated documentation samples) available for public consumption. Consume!

CP303 Interaction Design - a complete course on interaction design (although a horrid mixture of fonts). "Know the user. Know that you are not the user." Good stuff!

The 'Web ReDesign: Workflow that Works' online accompaniment houses a number of helpful web design process tools to download. While the tools are useful on their own, the book is a must read for all web professionals.

An excellent set of user-centered design case tools brought to us by Constantine & Lockwood.

Check out Sam Spade's suite of web-based network tools. So useful that they just helped me debug an issue with this site!