A free demo of Half-Life 2 will be released later today. Featuring some of the amazing digital actors and physical gameplay that has made Half-Life 2 the leading contender for Game of the Year 2004, the demo takes players through some of the early levels of the game and later transports them to the area of the game known as Ravenholm. The demo will debut on ATI.com, and requires a Steam account to install. For more information about Half-Life 2, please visit www.half-life2.com..
Edit: Seems like the download has been released, people are posting mirrors in the comments, but I will post the mirror I have handy which is the FilePlanet one. Its a hefty 751MB, the size of a decent game from a year or two ago! -ShortCutMan