1st Place 2008 : Marine diatoms,
Pleurosigma (200x) taken by Michael Stringer, Westcliff-on-Sea, UK. Stringer is not a microscopist by profession, but has been interested in diatoms for over 60 years, collecting them on Two Tree Island in the Thames Estuary, UK.
source:
http://www.newscientist.com/gallery/dn14971-small-world-gallery