Shape Collage is a free application that you can download for creating amazing looking collages. There are a bunch of applications/sites that do this kind of thing, but this might just be the best.
What makes SC so good is the ability to upload any shape (must be in png format) and then add your pictures. For example, I added the Apple Logo, and selected the photos I wanted to include in it.
Another great feature is that you can customize almost anything... draw your own shape, edit the background, save it as any kind of file, it's all here. Plus, it works on any platform!!!
Below is my Apple example....
Download Shape Collage by clicking here.