I recently spied the new book DIY Art at Home at my local library, and immediately added to my pile. It features 28 projects, all of which can be translated to pretty large scale wall art on the cheap.
Women's Day recently featured a full project from the book - a geometric triangle pyramid-y piece created with potato printing. The stamp is inked up every few rounds, so you get different levels of opacity as you continue to print. This is a pretty unique effect for such limited tools and technique.