The NASA Images site is so full of awesome that I think I'm going to bust.
Really, it is. Positively overflowing with awesome!
NASA Images is a service of Internet Archive ( www.archive.org ), a non-profit library, to offer public access to NASA's images, videos and audio collections. NASA Images is constantly growing with the addition of current media from NASA as well as newly digitized media from the archives of the NASA Centers.
The timeline on the home page is pretty slick, taking you from 1968 all the way up to 2008 with little thumbnails of significant items that pop up as you go from year to year. You can select a keyword to browse through (Gemini, Skylab, Apollo, etc) or choose from one of the four main categories above (Universe, Solar System, Earth, Astronauts) to start your journey. You can also search keywords on your own.
Browsing the images is pretty easy. On the left side are lists of keywords that you can click to narrow the selection of images displayed. Click another keyword and it's added to the search criteria list. Click an image and you're taken to a page that shows the image along with a bunch of meta-information about the image. Scrolling the mouse wheel while the cursor is on the image zooms in and out (or use the zoom selector placed over the image). Panning around a zoomed image is as simple as clicking and moving the cursor around. The box with the image meta-data can be expanded or collapsed when you're finished reading.
A potentially very cool feature is the ability to create your own media groups and presentations, allowing you to collect, share and show off your favourite images. You can also explore media groups and presentations that other people have created too.
Yeah, this is going to be a fun site to explore.