[opensource - POSIX] There is a sky. There are things in the sky. This program draws maps of things in the sky.
http://starchart.sourceforge.net/
Freeware for handheld computers to help find and track objects of the night sky.
http://www.startrak.co.uk/
Reports progress on their small-dish projects. Also provides related resource links. Based in South Carolina, United States.
http://www.draco.scsu.edu/radioastro.html
[open source - multiplatform] A module for performing astronomical computations using the Python scripting language.
http://www.rhodesmill.org/pyephem/
[commercial, Win/Mac] CCD camera control and image processing, includes SkyChart III.
http://www.southernstars.com/skysight/index.html
Online degree granting program in astronomy offering courses for Master of Science and Graduate Diploma of Science. Based in Melbourne, Australia.
http://www.swin.edu.au/astronomy/sao/
JavaScript calculator of sizes and distances of solar system bodies for making a scale model.
http://www.exploratorium.edu/ronh/solar_system/
An extensive astronomical learning system. Articles available at three levels: beginner, intermediate, advanced.
http://www.windows.ucar.edu/