Montage-a-Google is a cool little project that lets you create montages using Google's image search. It's fun and interesting and also can be used to create posters and pictures. It's fun and easy to use.
The web app does require Flash Player version 9 or higher.
There are examples of other montages and some tips and ideas on the site.
This could be fun to use in any classroom to create montage's of images related to a topic of study in that class. Students could create montages and other students would have to guess what the topic is based on the pictures.