These are interesting sites I like that may not fit into any particular category.
- Students for the Exploration and Development of Space — Don't let the name fool you; there is a lot here. SEDS was started in 1981 by Peter Diamandis while at MIT (and while we were roommates, little did I know...) but didn't really kick off as a major organization until 1987 or 1988. The SEDS web site has all sorts of resources including information on all the Messier and NGC catalogue objects, information on the constellations. How well these are covered varies considerably; e.g., Hercules has a very nice section whereas Lacerta barely gets an acknowledgement.
- NASA's Astronomy Picture of the Day — Each day a difference image or photograph along with a brief explanation and links to more information.
- Jack Schmidling's Astronomy Picture of the Week — Not in the same class as the NASA site, but he doesn't have the same budget either!
- Linux Astronomy. If you are a Linux bigot, er user, like me, this is a handy reference co-authored by the author of XEphem.