I'm sure you've already heard about it, so I'm a little redundant to bring it up — Carl Zimmer has a spiffy article in the NY Times about duck phalluses. No, that's not quite right; the most interesting part of the story was the bit about duck oviducts. Female ducks have been evolving increasingly convoluted oviducts to baffle the efforts of duck rapists to inseminate them, and male ducks have been evolving concomitantly long phalluses to thread the maze and deliver sperm to the ovaries.
I'd heard about these huge intromittent organs in ducks before, but this is another fascinating revelation: it took a woman scientist to suggest that maybe, just maybe, they also ought to look at what's going on in the female ducks, and then the whole wonderful story of coevolution of these structures emerged. It's actually a rather embarrassing instance of a scientific blind spot, where the biases of the investigators led them to overlook an important component of the story.