Built With: BuiltWith's goal is to help developers, researchers and designers find out what technologies pages are using which may help them to decide what technologies to implement themselves.
Consume, a volunteer group working to build a new network, one that is local, global, fast, expanding, public and user-constructed
Internet Archive, including the Wayback Machine, which lets you view web sites as they were long ago
Microformats: designed for humans first and machines second, microformats are a set of simple, open data formats built upon existing and widely adopted standards
OpenRBL: email "black lists" -- find out whether your domain is being blocked for spamming
Page2RSS: a service that helps you monitor web sites that do not publish feeds. It will check any web page for updates and deliver them to your favorite RSS reader.
RESTwiki: all about the REST (Representational State Transfer) architectural style for building web services, etc.
Lisp and Productivity: Despite the title, this is a discussion about the relative merits of continuation-based web programming vs. REST-based web programming.
Semacode: read real-world hyperlinks with a camera phone
CSS Pivot: Add CSS styles to any website and share the result!
CSS3, Please!: The Cross-Browser CSS3 Rule Generator
Open Source Web Design: the premier site on the internet for the sharing of web designs.
Open Web Design: resource for users with no design skills to quickly put up a site and showcase their content and as a way for designers to share their designs and showcase their talent
XRAY: a bookmarklet for Safari, Firefox, Camino or Mozilla. Use it to see the box model for any element.