For 38 years Nikon has been running the Small World photomicrography competition. The Dailymail and Popular Science have published an amazing selection of Small World photographs. The entire gallery can be found here. The deadline for the 2012 competition is April 30th, 2013.
The contest now includes also videos. Here is the 2011 video winner - ink injection into yolk sac artery of 72 hour-old chick embryo to visualize the beating heart and the vasculature:
Nikon Small World 2011 top 10 photographs:
More Small World videos can be found on one of Nikon's YouTube channels.