Most folks here use mostly glass and tile for their mosaics so I thought I'd bring up another possibility. What about creating mosaics with colored magnet tiles?!!

I started to get into this--you can find kits online with little colored magnetic tiles. My family and I mostly use these to create mosaic designs on the fridge but they can be used on any kind of magnetic surface.

One really cool idea that I want to try is to create a custom wall space for creating mosaic designs with the colored magnet tiles. You can do this by first painting a wall (or anything that doesn't already attract magnets) with magnetic primer paint, found at a store like Home Depot or online. Once the primer is dry, paint over it with any color(s) to match your decor. You could even put a cool frame around your new magnetic surface and wa-la, you've got a fun, custom area for creating and brainstorming and displaying your mosaic designs!!!

I think this would be a lot of fun in a kids room too!