Also, just for kicks, if you have steam and nowt else (req. Nvidia based graphics), you can get a slice of portal and HL2:DM. Free!
Linky!
If you don't have Nvidia based graphics (You bad, bad, ATI person), you can get the same stuff from here... yeah.
Linky!
I'd follow those through and check they're not exactly the same, but... it's late.