Don't underestimate MS Paint, you guys! I actually made some pretty good promo posters on it for my anime club years ago. I still remember making a promo poster for "Pizza & Turtles" night for my club's special screening of the original Teenage Mutant Ninja Turtles cartoon at my local sci-fi convention. You can also import special fonts and high quality screenshots into it.
Hell, I also made some mock screenshot edits for Langrisser II for the Genesis on Paint just so I can show off my skills at the Hiryuu Honyaku game translation forums.
In short, MS Paint rules!