Darwin exhibition at the Natural History Museum

http://www.nhm.ac.uk/visit-us/whats-on/darwin/
"Darwin is the biggest ever exhibition about Charles Darwin. It celebrates Darwin's ideas and their impact for his 200th birthday in 2009. Discover the man and the revolutionary theory that changed our understanding of the world. See incredible, revealing and rare exhibits, some on display for the first time"

There is a slideshow of some of the exhibits here http://www.nhm.ac.uk/visit-us/whats-on/darwin/slideshow.html and also links to an interactive Beagle voyage and a video of Darwin's mocking birds.
Natural History Museum 14th November 2008 - 19th April 2009
The Natural History Museum also has a web site for Darwin's 200th birthday detailing national events http://www.darwin200.org/

While you're at the Natural History Museum you might also want to catch the Wildlife Photographer of the Year exhibition http://www.nhm.ac.uk/visit-us/whats-on/temporary-exhibitions/wpy/ 31st October 2008 - 26th April 2009