ProCollage (US$1.99) is a very nicely done app for creating photo collages on any iOS device. After you grant access to your camera roll, PhotoCollage lets you select multiple images and use pre-defined templates. Don't care for those templates? No problem, it lets you use a free-form approach as well.
Images can be moved within a frame, resized or rotated. Frame colors are almost unlimited, and there is a selection of multiple backgrounds for your images. Happily, the app doesn't make you purchase anything else to make it all work.
This latest version adds the ability to apply text to a collage, and there are 14 different styles. Putting the app to a test today, I found it easy to create a variety of nice looking sets of images. There is help built in, but I really didn't need it.
One thing lacking is that the app does not work in landscape view. If it did, some wide-aspect-ratio images would be larger on screen, allowing for more precise placement.
ProCollage seemed well behaved under the iOS 7 beta, and currently requires iOS 5 or greater. It has been optimized for the iPhone 5.