If you're looking for a different way to present photos, especially on posters, AndreaMosaic is a free photographic mosaic creation program. It's great for sports teams, international field trips, or even for the school yearbook.
Basically you give it the image that you want to create, then a lot of other images to use as tiles. There are a few settings to tweak if you'd like, and the images it creates are very cool.
On the Mac, there's a similar program called MacOSaiX.