Today, Sierra Studios and Valve Software made available a patch that upgrades Half-Life to version 1.1. This new version includes upgraded networking code, the multiplayer mod Team Fortress Classic 1.5, and developer tool updates - including the Worldcraft 3 level editor. Team Fortress Classic 1.5 features three new maps (Dustbowl, Epicenter, and Warpath), new networking developed for the upcoming Team Fortress 2, and a new in-game command interface.
You can get the patches from GameSpot's Half-Life downloads page.
The popular Half-Life counterterrorism team-play mod, CounterStrike, has also been updated to work with the 1.1 Half-Life code. The new 6.5 beta includes new weapons, maps, a smoke grenade, and a system for in-game map voting. You can download CounterStrike from GameSpot's affiliate, 3DFiles.com.