Is there any good apps for creating cool pictures/ collages on iPhone? Free btw?

I want an app where you can create cool images, like put image on top of each other and crop one smaller or make it smaller so it is on the other image, you know what I mean? Kinda like a collage but not

*Are* there any good apps for that? I don't think so. There are plenty of images out there, but you can't put one on top of another as far as I know.

This is what I have for putting photos on top of each other http://www.softdd.com/mobile/pic-overlay/index.html?y2