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
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
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.