I am loving this app, Phototropedelic. Think it is iPad only, it is supposed to be a quick and easy way to make your photos look like a Peter Max poster or something, complete with stars, rays, and bright vivid colors. But, there are tons of customization options, which I exploit to either simplify busy pics, or busy up drab ones. The end result can come out as a pretty decent illustration.
It takes some preparation to get the results I want, usually tweaking contrast and color balance. One nifty side benefit is the fact that you can use low resolution photos and come out the other side with a decent image.