There's an article that came out today in Current Biology that documents very rapid vertebrate evolution, in stickleback fish. Has some very interesting implications regarding the rapidity with which organisms can respond to abrupt environmental shifts, especially valid given our ongoing planet-wide experiment in that topic:

http://www.current-biology.com/content/article/abstract?uid=PIIS0960982208005125

There's been some discussion about it on io9, too:
http://io9.com/391018/rapid-deevolution-creates-lake-of-fully+armored-fish-in-just-50-years