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

The three-pin version (non-PWM) is referred to by some computer technicians as a "TX3 connector," but this is something of a misnomer (similar to the moniker "Molex connector," referring to the once-common 4-pin ATX power connectors originally produced by AMP).

The standard 3- and 4-pin fan connectors are Molex KK series connectors. According to Wikipedia the part numbers for the 4-pin version are:

• Female Housing: 47054-1000
• Female Contacts: 08-50-0114
• Male Header: 47053-1000

Of course, many manufacturers produce compatible connectors, and most 0.1 inch pitch headers will work with these connectors provided they are long enough (approx 0.3 inch).