Astronomy Magazine Kalmbach Publishing.
A rich site, full of astro-info, the latest news, an "observer's guide," and more.

Sky & Telescope Magazine Sky Publishing.
The magazine and a lot more. One of the most comprehensive astronomy sites on the web. Includes Sky Publishing's on-line catalog. Also, software, product reviews, news etc.

Astrophysical Journal The University of Chicago Press, 5801 S. Ellis Avenue, Chicago, IL 60637

PASP Publications of the Astronomical Society of the Pacific
Lots of resources for educators.

Mercury Magazine
Official periodical of the Astronomical Society of the Pacific. "...communicating astronomy to the general public."