The latest Don't Panic poster artist to provide free art for your walls is Pure Evil, on the theme of Imagination. Maybe best know for the fanged bunny, he's fond of spraying on the walls of London. He also has his own gallery/art space/music studio on Leonard Street, which opposes artists as commodities and shoots curators on sight.

http://www.dontpaniconline.com/magazine/imagination/pure-evil---imagination-poster-artist