For the past eight years, Olympus America has sponsored the Bioscapes Competition for the most beautiful and/or extraordinary microscopic images. The winning photographs must "depict subjects that are, or at one time were, living".
Here's the 2011 Grand prize winner, by Charles Krebs of Issaquah, Washington, USA:
Specimen: Rotifer Floscularia ringens feeding. Its rapidly beating cilia (hair-like structures) bring water containing food to the rotifer
Technique: Differential interference contrast microscopy
I happen to like this Honorable Mention entry by Gerd Guenther of Duesseldorf Germany:
Specimen: Stem section of Fragesia sp., garden bamboo, showing a vascular bundle
Technique: Fluorescence, ca. 200x
You can see the full gallery of winners here.
The deadline for next year's contest is Sept. 30, 2012. If you're interested in entering, you can read the rules here.