I enjoy when RPG companies provide updates or chat on Twitter (this is me, by the way). I have a few I follow that folks may not have realized are online. (There are also plenty of game designers and personal accounts, but for privacy's sake I'm not going to list them here):
Mind Storm Labs
Troll Lord Games
Are there any "official" Twittering RPG companies you follow that I've missed? I'd like to get a nice full list of RPG company twitter accounts.