Sites worth checking out:

Eye of Science	Photographs of the smallest elements of the micro world.
Snow Crystals	Snowflakes like you've never seen them before.
Earth as Art	The Earth seen from a satellite.
Luminous Landscape	An invaluable photography resource.
Astronomy Picture of the Day	A new astronomy-related photo every day.
Family Radio	See the Creator of such beautiful landscapes.

It's not photography, but it's still neat:

Julian Beever's Pavement Drawings

Amazing what you can do with some chalk.