Museum of the History of Science at Oxford University
(http://www.mhs.ox.ac.uk)
Covers almost all aspects of the history of science, from antiquity to the early twentieth century -- particularly strong in their collection of scientific instruments, including early mathematical instruments -- Online exhibits include Compass and Rule: Architecture as Mathematical Practice in England, 1500-1750, The Measurers: A Flemish Image of Mathematics in the Sixteenth Century and The Geometry of War, 1500-1750 (see 4 links below).