I've been playing roleplaying games (mostly D&D) for more than 25 years. Since D&D has pride of place in my own experience, it also gets pride of place here--right now it's the only subcategory that's up and running. I intend to add more subcategories for other games I've played (Traveller and GURPS are on the list right now).
D&D and d20: The one that started it all (at least for me).
PT Games, Inc.: The website for the publishing company owned by myself and Tim Plum.
On the subject of publishing, specifically electronic publishing, several of the articles in the Computers category of this site are relevant, since many RPG products (including those of PT Games) are published in electronic form. In particular, my article on Digital Rights Management discusses why I think it's not a good idea for e-publishers to adopt.