Sell sheets seem to work really well indeed. The goal is to fit everything that you want to communicate about your idea on a single sheet of paper, hence the name “sell sheet” (or “one sheet”, as I’ve seen many people call it).
I mainly use Fireworks for the graphics, it’s very similar to Photoshop. But there are free tools out there, like Gimp. You could also use Paint but I find it so time consuming! Also, I recommend printing on glossy picture paper, looks much more professional.