We don't often do contests or broad promotions, BUT we have started occasionally sponsoring larger streams. There are a few broadcasts that end up in the thousands (and tens of thousands in folks watching the archives) that we've popped in and "sponsored" and episode or two, and we'd like to do some more of that. It's nice in that it ends up being folks who are already plugging Roll20 getting some clear sponsorship to take a moment and... well, plug a bit more directly. If someone has a large stream and would like to be considered for that, feel free to contact me. And if you're just starting out, but looking to grow your audience some, we're usually pretty enthusiastic on Twitter about sharing folks using Roll20, so be sure to send a tweet our way!
