We collected a whole bunch of different coloured leaves to do leaf printing. It didn't turn out quite as well as I thought, but it was fun, nonetheless.
We put the leaves on a piece of watercolour paper and then covered them with paper towel. We got out the toy hammer and started pounding. My 3 yr. old son especially loved that part!
The end result...
My inspiration: http://buildmakecraftbake.com/2009/04/how-to-hammered-flower-and-leaf-prints.html