Edit: the website states today that it's only available in the US.. oh well.
If you're one of the two people who still don't own this game, they're currently running a limited time promotion connected with a campaign in the US to help with dental health, "Stop Zombie Mouth!"
Go to http://www.stopzombiemouth.com/ and you can download coupons to give out that have a code on them to redeem a free copy of the game from October 30th to November 10th. I don't think there's any catch, other than you might have to make an account at Popcap.com I guess.
The code is PEAH8R.
Enjoy - I used to play it in between wipes in raids
Cog