The Virtual Observatory features an impressive collection of images of "deep-sky" objects: galaxies, nebulae, and clusters. Included is the full Messier catalog, NGC, Herschel 400, and other lists of objects. The well-organized lists include detailed information about the location, class, and brightness of these objects, and many images of these objects are available.

http://www.ifi.uio.no/~mikkels/astropics.html

The Virtual Space Museum seeks to display the manned and unmanned spacecraft of Russia and the former Soviet Union. At the site you'll find information, including some excellent images and VRML virtual-reality models, of Russian spacecraft from Sputnik to Mir, and some spacecraft, liked the planned lunar landers, which never flew. The site is short on encyclopedic text information, by design: the creator wants you to see Soviet and Russian space history, and does an excellent job displaying it.

http://www.ccas.ru/%7Echernov/vsm/main.htm

Some of the most intriguing phenomena observed in the sky recently are sudden, brief flashes of light, bright enough at times to outshine Venus, the brightest object in the sky after the Sun and the Moon. These flashes have been traced to spacecraft in the Iridium global communications satellite constellation. The flashes of light appear to be sunlight reflecting off the highly-polished aluminum main antennas of the spacecraft. This site, part of the larger "Visual Satellite Observer Home Page", has more information on this interesting phenomenon and how to determine when one might be visible in your area.

http://www.satellite.eu.org/sat/vsohp/iridium.html

Over the last 35 years, American spacecraft have imaged every planet except Pluto in great detail, as well as dozens of moons, asteroids, and comets. These images are brought together in one site at JPL's Planetary Photojournal. You can choose the planet or moon you want to see, and from what missions you want the images. The site then displays the desired images, which can also be viewed in greater detail in a wide variety of formats. The images here come directly from the original spacecraft data, and often look much better than identical versions elsewhere on the Web.

http://photojournal.jpl.nasa.gov/