Nikon's homepage, a gallery at The Guardian, or at Boston.com's The Big Picture.
Pictured above -
The eyes of a mayfly (Laurie Knight, Tonbridge, Kent, UK)
A butterfly egg on mimosa buds (David Millard, Austin, Texas)
Light refracted in a soap film (Gerd Guenther, Dusseldorf, Germany)
Crystals of cacoxenite (a phosphate mineral) (Honorio Cocera-La Parra, Valencia, Spain)