One of my favorite lessons I did this past school year was whimsical trees inspired by the story Willow. (I know I saw this on another art education blog, so please let me know if it was you so I can give you credit).
After reading the story we looked at several tree pictures and discussed how we could come up with our own creative trees. Each student received a piece of 12x36 paper (I think this size really contributed to the overall success of the project). We began with tempera cakes and then used pre-mixed tempera paint.
The kids really seemed to enjoy the process. I loved how they turned out!