The US government: A great source for great photos?

Artists are always looking for new sources of images. I've long been aware of NASA's massive image libraries; I used some of their images in a printmaking project my senior year. But today, while searching for a photo of a sea otter to show a coworker, I came across NOAA's Photo Library. It's quite impressive; I recommend browsing by collection (click on "Navigating by Collection" on the right side of the page) just to get a feel for what' available.

This got me thinking. How many other government agencies have images freely available on the web? A quick Google search answered my question. U.S Government Graphics and Photos is a directory of links for the image libraries of many federal agencies and departments. Not all of the images are public domain, nor do they all have high quality, high resolution images.(NOAA and NASA both do.) But it's still a great resource.

A few of interest:
Geological Service's Astrogeology Gallery
National Oceanic and Atmospheric Administration (NOAA)
Grand Canyon National Park Photos (image above is D_1258)
Hawaii Volcano Observatory (interesting photos; hard to navigate; lower resolution)
Public Domain Tornado Images (National Severe Storm Laboratory)

Some NASA image databases:
NASA Multimedia Gallery
Solar Eclipse Images
Visible Earth