While I have previously expressed my views that almost certainly too much attention has been paid to the eugenic discourse in the early C20th and seldom enough to other less clearly focused and visible movements based on a more environmentalist/improvability of the human product philosophy, I'm still very excited indeed about this project at the Wellcome:
Papers of the Eugenics Society to be Digitised
This is an extremely significant collection which has a lot to offer beyond the mere story of eugenics in the UK. True, it's had a lot of use over the decades since it was acquired and catalogued by what was then the Contemporary Medical Archives Centre at the Wellcome Institute for the History of Medicine, but there are still quite a lot of areas that have not been explored as fully as they might be. For an indication of some of the work that's already been done, see the Birth Control/Eugenics bibliography: secondary works (pdf)on the Wellcome Library website.