I do this sporatically, but I am giving away free D&D stuff to people who participate on this site. There's no promise of when and where I will do this, but it does happen.
Also, some ongoing things that I do is give stuff away each month for blog contributors. Ask around and you'll see what's been given out.
Be sure to contribute, and you'll find yourself increasing your chances.
*Note: As of 01-OCT-2011, I will only be giving away prizes to those who living in North America. I've run into major issues getting crap sent out internationally and I just don't want to deal with it anymore.