The Behemoth (Castle Crashers) have released a trailer with early footage from their next game, codenamed Game #3, on vimeo. A 2D platformer with one or more twists and co-op seems to be what they are working. The game has no proper title, and no platform has been announced. There is a tentative 2010 date at the end of the video, but that's all we've got for now. But it certainly looks like a lot of fun...
Check out Game #3 on vimeo