This list is hardly comprehensive and your best bets for a large list are the websites run by Sky and Telescope or Astronomy magazines. I'm not so hot on the latter website simply because it confuses Netscape under Linux so badly that I not only can't view anything on their site but afterwards I have to kill Netscape because it won't display anything from any site.

Because my own list of resources is growing, I've tried to organize them a bit here. Tried is the operative word.