Modifications and Add-Ons

Admin Mod
Offers news, overview, FAQ, installation guide, list of commands, help files, scripting, forum, and downloads.
http://www.adminmod.org/

AdminNow
An add-on program that allows server operators to better control game parameters. With instructions on operations, news, and forum.
http://www.adminnow.org/

AMX Mod X
Provides user-created administration tools through a secondary scripting language. Includes downloads, forums and a plugin generator.
http://www.amxmodx.org

The Black Mesa Facility
Reviews, FAQ, game information, downloads, and links.
http://www.geocities.com/re3_nemesis1999/

Bullseye Crosshairs
Replacement crosshairs for Half-Life with instructions on installation.
http://www.bullseyecrosshairs.com/hlsites.shtm

Half-Life Reloaded
Shockwave online version of Half-Life.
http://necromanthus.com/Games/ShockWave/half-life.html

The Ship
Includes news, downloads, a manual, movies and screenshots.
http://www.theshiponline.com/

Sven Co-op
An online cooperative Half-Life modification where players fight against AI controlled enemies.
http://www.svencoop.com/