Electronic Arts' On the House program for Origin lets users download free games for a limited time and keep them. It is obviously a way to get the service installed on more computers, and it's EA so some people are going to complain about that, but I'm a fan of the promotion.
Past titles have included Dead Space and Plants vs. Zombies. Right now, through June 3, it's Battlefield 3. Go crash some jets, for me. (So I'm not the only one embarrassing himself.)