Planet Half-Life - Should be obvious, but they are the source for all news related to the Half-Life series. 69th Vlatitude - An awesome archive of tutorials and resources.  Also sports an active forum full of interesting and colorful people. Nightwatch - the competitor of the original Dark Truths.  Several ex-team members joined them.  Go and see! Sourceforts - A Half-Life 2 mod that also hosts out forums.  Thanks alot, jlf! Half-Life Improvement Team - A collection of damn talented individuals who are dedicated to revitalizing the aging Half-Life and its PC expansions with upgraded models and graphics.  Most of the stuff is on the forums, though.