Bruce K.
Yelp
A very interesting museum, the Wellcome Collection (named after Sir Henry Solomon Wellcome, founder of the UK's largest charity) has a science and medicine theme, with collections that vary throughout the year. When I visited, the ground floor's special exhibition was focused on identity - who we are, or at least, who we think we are. By focusing on 9 lives, they present a thought provoking array of historical and contemporary ideas about the self and personal identity (quoting from the handout).
With displays and biological stories selected to make you think (ouch!), they included April Ashley (who had one of the first British sex-change operations), Frank Joseph Gall (who termed the 'doctrine of the skull' that later became known as phrenology), and Charlotte and Emily Hinch (biologically identical twins, though born years apart due to IVF). I was most interested in the display of Sir Alec Jeffreys, who was the pioneer of DNA profiling. (It made me think of CSI!) Lots of interesting technological displays as well as material from his own personal identity. Really cool stuff!
On the first floor ('second floor' to Americans), the Medicine Man collection displays a large number of Sir Henry's own items as well as a good number of interactive and audio-visual exhibits. I was most impressed with the printout of the human genome, a dozen or so shelves of massive tomes, all printed with really small G's C's A's and T's. Wow, people are complicated! Don't skip the "Obesity" and "Malaria" sections, which are an interesting contrast, the former affecting mostly developed nations with cheap high-calorie foods and the latter affecting the developing world that doesn't have the technology or funds to fight it.
There was also a collection of the Wellcome Image Awards of 2009, a really interesting display. Check out http://www.wellcomeimageawards.org.
And when you're done with all of that, there's a book store/gift shop with the usual trinkets and gewgaws you would expect for a museum including purchasable prints and postcards with images from the collections.
Not had enough? Try the well stocked (and slightly above reasonably priced) cafe and shop, with coffee, pastries, sandwiches, salads, soup and even beer and wine. (After the obesity display, I wasn't particularly hungry.)
Sadly, visitors are not permitted to take pictures of the exhibits. There are a number of images on their website (linked at the top of the page). Admission is free and there are occasional guided tours.