Two very good articles: the shorter one, with a clear emphasis on Darwin's contributions, is by Olivia Judson, and the longer one, with some details about the prehistory of the idea of evolution is by Richard Conniff [via Jason Kottke].
The interest in Darwin and his big idea has been rekindled now because, as Judson explains,
... July 1, 2008, is the 150th anniversary of the first announcement of his discovery of natural selection, the main driving force of evolution. Since 2009 is the 200th anniversary of Darwin’s birth (Feb. 12), as well as being the 150th anniversary of the publication of his masterpiece, “On the Origin of Species” (Nov. 24), the extravaganza is set to continue until the end of next year. Get ready for Darwin hats, t-shirts, action figures, naturally selected fireworks and evolving chocolates. Oh, and lots of books and speeches.