Bill Venners' artima site is an excellent resource for programmers who strive to improve their knowledge and ability. It features interviews with, and blogs by, software innovators and thought-leaders.

VersionOne is the leading project planning and management tool for agile development.

Scheduling Software - Scheduling software for managing people and resources. Free evaluation version.

The Agile Alliance began with the signatories of the Agile Manifesto, and continues to maintain ties between those involved with XP and the other agile software development methods.

Scott Ambler's Agile Modeling site is the central source of information on software modeling in an agile fashion.

Modeling Style is Scott Ambler's site of tips and techniques for creating better software diagrams.