If you've been a fan of almost anything Telltale Games has ever done (and really you should be) then the teaser trailer above is going to get you pretty darn randy in your nether reasons. The teaser is short and sweet, but should get many an adventure fanboy pretty excited for what Telltale is cooking up, especially when it says "Bet you never thought these guys would ever get together."
But who are "these guys?" Let's do some deduction from the silhouettes we have. I think Max from Sam & Max is blatantly obvious and if that isn't Strong Bad on the far right then I'll eat my own shoe. I'm also pretty sure that the fellow on the left is Tycho from Penny Arcade. All of these characters have, of course, been the subject of a Telltale adventure game, but what about the big fella? Doesn't he look like a heavy from Team Fortress 2? It does make sense as Valve and Telltale have been working and playing together for a while now.
Updated: As DinnertimeNinja pointed out, Tycho wasn't in a Telltale game as On the Rain-Slick Precipices of Darkness was made by Hothead. Sorry about the mix up.
Telltale Teases Crossover Game [Game Stooge]