I took a look at Diptic a while ago and liked what I saw. The US$0.99 universal app allows you to select photos from your camera roll and create compelling collages that can be sent at various resolutions to family and friends.
The new version 6, just released, has a great many new and enhanced features, including more than a 100 new layouts, textures on borders and the ability to add captions to photos. It offers much more control over frames and the arrangement of images.
One welcome addition is improvement to the photo picker, and for the first time you can now select multiple images at once, rather than going back and forth to your camera roll. The app now supports the Retina display and is optimized for the iPhone 5.