What is the name of this connector from a fan?
I think that it could be Molex 47054-1000.

Found it in section 4.1.5 on page 17 of this doc: http://www.formfactors.org/developer%5Cspecs%5Crev1_2_public.pdf

Here is a Molex product page: http://www.molex.com/molex/products/datasheet.jsp?part=active/0470541000_CRIMP_HOUSINGS.xml