I really like this look by Zooey Deschanel even though I realize it's not natural:

But as far as real, natural curly looks, it'd have to be Linnea Jönsson's hair (from Swedish band Those Dancing Days). I love the frizzy, rock 'n' roll, don't-give-a-crap look (it's what I'm going for at the moment actually except mine's a bit shorter):