Note: I'm including this activity, even though I continue to struggle to get it to work myself. I like the idea, and know that crystals can be grown from each of the following solutions, even if I can't grow them. I can grow great Borax and Alum crystals. The rest of them... not so good. If anyone has any advice, please pass it my way.
Consider making up a set of crystal sticks so students can see some of the different shapes crystals can take on.