My favorite new instrument at school is definitely the egg shakers. I priced them at $2 each at a local music store, but then decided to make them much cheaper using Easter eggs and rice.
After a few uses, I must say that they are definitely my favorite rhythm instrument right now, for these reasons:
1. Even with 15 students shaking them with all their might, they still aren't that loud.
2. They fit in the students' hands perfectly, and you know what they say about idle hands...
3. The students love them.