FEI is a company from Oregon that makes electron microscopes. FEI is the sponsor of a yearly contest, to find the best electron microscope images. Here are the top 3 entries. You can find all entries available in desktop wallperpaer-sized versions on Flickr.
First position: Microcanyon. Microcrack after bending test, colored by Manuel Paller. Courtesy of Martina Dienstleder.
Second position: Alveoli. Capillary net of a alveola showing the erythrocytes within the blood vessels. Courtesy of Oliver Meckes.
Third position: Lamnacarus ornatus. Forepart of a mite, coloured by Margit Wallner. Courtesy of Angelika Reichmann.
Here are some more interesting photos that i found there:
Radiolarian. A fossilized single cell organism from the Barbados Islands. Imaged gold coated and coloured in post production. Courtesy of Linnea Rundgren.
Radiolaria Polycystinea. Fossilized, ancient single cell organism, from the Barbados Islands. Imaged in low vacuum mode after having received a thin gold coating. Courtesy of Linnea Rundgren
BIO-NANO-SYMBIOSIS. Dehydrated and critical point dried Human Monocyte labelled with 12nM Colloidal Gold Particles. Credits to: Dr. Chandrasekaran Nagaswami, Dr. Lubica Ravova, Dr. Lolita Rotkina and Professor John W. Weisel, Ph.D. Dept. of Cell & Developmental Biology Univ. of Pennsylvania School of Medicine. Courtesy of Lolita Rotkina
Silver and copper.Silver nanorods and particles growth on copper crystals. Courtesy of wadah mahmoud
Tie-Dye Leaf. Image of the veins running through a cross section of a leaf. Student image courtesy of Daisy Lee. Courtesy of Craig Queenan
Parasitic Mite on Moscito Larva. Mite on a Moscito Larva from a German Lake. Courtesy of Nicole Ottawa
Iron egg shell. Iron nodule as egg shell filled with calcium carbonate. Courtesy of wadah mahmoud