Try HL2 FREE

If you're still one of those waiting to try hl2, either to see if you like it or to see if it will run on your 'puter, the half life 2 demo is here! You can run around as the freeman and blast monsters and stuff... 56k users beware because its seven hundred megabytes.

Note: If you already have Steam installed and have an account you do not have to download the 750MB demo. Simply restart your steam client and you will see an option to preload/download the Half-Life 2 demo. Downloading the 750MB demo prompts you to create an account, even if you already have one.