I've seen a lot of collage software come and go. Some are quite powerful and keep growing, such as Diptic. Others don't really have interesting templates or don't allow you enough creative freedom to let you make the collage that fits your mood or your personality.
The last few days, I've been playing with a free app called Fuzel, and it helped me create some striking collages. Best of all, it gave me the flexibility to move and transform the elements without being restricted to stiff templates.
Fuzel starts off with a quick tutorial, then it's time to open your camera roll and select some photos. There are plenty of templates, but the best ones are the ones that aren't just a bunch of rectangles bolted together. You can cut and divide the frames into smaller ones; you can merge frames into a single frame; and you can drag the borders around as you please. I was happy to see my new collage was saved at full resolution, but there are smaller options when you are mailing them or sending them to social networks. Swiping the screen will undo your last change, and a collage can be saved to edit later.