Half Life Source
Offers news, guides, screenshots and a forum.

Half-Life Portal
Includes guides, walkthroughs, reviews, and a forum. Also offers a media area with videos and screenshots.

Half-Life Prototype Developers
User submitted articles on the Half Life series. Includes tutorials on server administration and mod development, and technical articles on the game engine.

Planet Half-Life
Resource includes files, forums, modifications, articles, and daily news.