I'm sure by now everyone has seen the brief Half Life 2 video (and if you haven't, go get it). I don't have the bandwidth to provide it, but I heard a little birdie say that the 500 meg .mov was uploaded to the usenet newsgroup alt.binaries.multimedia. I've watched the first half of the 15 minute video and all I have to say is wow. This game is going to completely and totally kick ass. The physics engine alone will be worth the price of a computer upgrade (and the game itself of course!).
So run, don't walk to your newsreader and search for "half" in you-know-where and start downloading (it's in rar format and pars are there as well.