These are both tower defense types of games. Registers on Steam.
Oh also as an IGN Prime member you get 15% off purchases at Direct2Drive. Make sure to disable the auto-renew option when you sign up. You can cancel right away and your membership stays active for the 30 days so you can still take advantage of the 15% off. Might be a good way to pick up Skyrim for a good price.
UPDATE: They’ve ran out of CD Keys for Orcs Must Die! Sanctum DLC is still active however.