There is a really cute video clip on teachertube about the rock cycle. It shows an experiment using crayons. This experiment is actually really easy to do and the kids LOVE it!! That would be a nice lesson. Just type rock cycle into the teacher tube search and it will come up.
I also always do a rock lab. I have them wear real science goggles and go around to different stations. They have to identify which rocks are at that station and draw them. One of the stations is always a dig, where they scratch away to discover rocks below. Archeological digs can be purchased at any teacher store.
I Also have a science CD that has a song about the rock cycle that is really cute. It makes learning the cycle fun.