A little dated, but there are still many good links there. From Cornell University.

Over 2,400 annotated resources around the Web to HTML, CSS and color charts, font sites, search engine optimization sites, graphics and HTML tutorials and programs, usability and information architecture sites, informative articles, tips, and more.

Thousands of XML and Web development related resources indexed alphabetically. Naturally there are lots of XML links, but also includes listings for accessibility, CSS, DOM,...too many to mention here. Each category has a "jump to" alpha/title index.

Not a directory in the traditional sense, rather an RSS feed aggregator for Web developers. Keep up to date with the latest blog posts, reviews and articles with fresh content every day. Excellent idea, good work Pete.

A large collection of resources for Web developers and programmers with categories that includes C/C++, Flash, HTML, Java, Javascript, Perl, PHP, Python and XML. Sub-categories include articles, tutorials, software, scripts and programs, and books.

Jots is a social bookmarking site similar to del.icio.us, only the userbase is mostly developers so there are tons of categorized resources to browse. Built with Ruby and PostgreSQL, it has a clean and easy to use interface. Anyone can create an account.

The simple interface, an alphabetical index, is deceiving. This directory has an exhaustive set of resources in every conceivable category. And this is just the programming branch of the directory, visit the top-level view for countless more categories.

Powered by LAMP and the Symfony PHP framework, with tagging and Ajax features, Listible is a list of lists, many of them relevant to the categories in this index. Anyone can create an account and start a list. Voting drives the best resources to the top.