As you have probably noticed, I have listed a few open source programs as resources.  I have to say that I absolutely love perusing the absolutely gigantic open source program listing on SourceForge.  It would take forever and ever to look at each program.  You can't really do that easily since it is such a massive database of open source projects.  I go on there every now and then to look for this or that, and I can usually find some gems.  Today is no different.  I hope you enjoy these two as much as I have.  Anytime that I take the description from the website in question, I italicize the text.

Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.  Just set your coordinates and go.  It is absolutely beautiful and easy to navigate.  If you are having problems, they have a forum and some great user's guide.  It's a pretty hefty size if you are downloading with a dial-up connection.  This will be great when we start working on Astronomy.   I cannot say enough about it.  You can overlay the drawings of the constellations, the names of the constellation, the art of the constellations, names and locations of nebula.  You can search for a particular system.  It goes on and on.

FreeMind is mind-mapping software.  These are great for you and your students to organize thoughts for essays, papers, homework, working out problems, planning projects, etc.   This little program is just as good as any mind-mapping software out there, and best of all, it's free.  One thing I really liked about the program is the ability to change the appearance of the interface.   I know, that's a bit trivial, but that's how I am.  I played with it a little bit, and it seems very intuitive to use.  I think it is a definite must-have for any homeschool.