Yes, counter-strike 1.6 (not source) completely free!
Steam Client including Counter Strike 1.6
Steam is Valve's new way of getting games into your hands ASAP. Games like Half-Life, Counter-Strike, and Counter-Strike Condition Zero are all being made available through Steam.
Steam games are automatically kept up-to-date with the latest content and revisions. Steam also includes an instant-message client which even works while you're in-game.
At its core, Steam is a distributed file system and shared set of technology components that can be implemented into any software application. Steam is a broadband platform for the deliver and management of digital content, currently features a variety of Valve games including Counter-Strike 1.6, which introduces the new riot shield, the official CS bot and more.
- Play the latest Valve games (like Counter-Strike 1.6 )
- Get automatic updates (no more patching!)
- Chat with friends, even while you play
- Find the best servers & find your friends' games
- Receive Steam-Only special offers
Note: You have to create a steam account to receive the game.