A good summary of religions of the world can be found here.
This website is more appropriate for children to explore themselves.
This website categorizes religions of the world quite neatly.
Some free powerpoints can be found here, although some of the links no longer work.
This looks like an interesting book, especially for children. A full reading list can be found here.
This PBS website on world religions has a number of excellent links, mainly for older students but would make excellent background reading for teachers.
I'd love to buy these posters for my room, but they are a little expensive!