Nora (2.5) loves to create artwork on the tall fences in our yard- we use sidewalk chalk, homemade fingerpaints, dumped out bubbles...pretty much anything that would leave a good mark. It distracts her nicely from creating the same kind of artwork on her sister Susannah (6 months).
The only downside? The fences aren't in the BEST of conditions, so occasionally markings get embedded deep into the soft wood. But I think that looking out the window and [permanently] seeing a toddler's attempt at drawing balloons is a pretty nice start to any day, don't you?