Ned Wright’s Cosmology Tutorial: A great resource for all sorts of cosmology news and information.
Frequently Asked Questions about Black Holes (shameless self-promotion!)
John Baez’s web site, which is full of information about a lot of different topics in mathematical physics. The parts I’m most interested in are the ones about general relativity and gravity (and not just because I co-wrote some of it.)
For technical articles about astrophysics and cosmology, the place to go is the astro-ph arXiv.
For great astronomy pictures, you can’t beat NASA’s Astronomy Picture of the Day.
Update: These are now listed on the blogroll (over on the right), which is where they belong.
That’s a great question. As it turns out, black holes do radiate like blackbodies. That’s the phenomenon known as Hawking radiation. Hawking radiation is a quantum-mechanical effect, which I try to explain in my Black Hole FAQ, although I have to confess that that explanation is very vague and imprecise.
As I understand it, when he came up with the idea of Hawking radiation, Hawking was thinking about (among other things) apparent contradictions with the second law of thermodynamics as it applies to black holes. The details of this are pretty hazy to me, though.
I should add that Hawking radiation is a theoretical prediction that has not been confirmed by experiment or observation. The theoretical arguments are considered very robust, though.