I had fun with the different mediums on this one. I really like the black marker outlines with colored pencil inside. I just have a very cheap set of colored pencils, but even with those it was fun to mix them to try to match the coloring on my fall leaves. I also learned something about leaf veins by looking closely at my leaves and picking out the major ones to draw with marker. The crayon contours were relaxing to draw--I just did one line around each leaf and then cycled around again to do the second, third, and so on. I like the energy they add, and they make me think of leaves falling in a pool of water, sending out ripples in every direction.
Here's a link to the original idea and instructions at Art Projects for Kids.