The Anthony Nolan Trust keep a register of potential bone marrow donors for people who need a transplant, more information here:

http://www.anthonynolan.org.uk/about/what-we-do.htm

I am running the Yorkshire 10k for them in September and would appreciate anything at all you can afford to donate:

www.justgiving.com/kathyatkinson

I've only just set up my page so if you're quick you could be the first!

Thanks :)