Plum Amazing has PhotoMatte, a new theme based app for Mac OS X that focuses on photo layout. To use, you pick a theme, drop in your photos, and export.
PhotoMatte comes with 48 templates, 39 backgrounds, 171 objects (like sunglasses, baseballs, etc.) to enhance your creations, over 25 frames, 17 effects (from blur to over masks to gradient maps), and 15 video tutorials. It provides multiple export and sharing options.
PhotoMatte requires Mac OS X 10.8 or higher. It costs US$30 can be downloaded at http://plumamazing.com/mac/photomatte.