Well, seeing as my other 'hat' is astronomy, I might as well put down some of the wealth of astronomy goodies available for free. Nearly every amateur astro in the business sings loud the praises of
Stellarium, which gives you an excellent picture of the night sky which you can start to use in anger even if you've barely even glanced at the moon. I personally tend to pass over it in favour of
Cartes du Ciel which is my favourite, albeit a bit more technically-oriented and not so pretty, but that's what suits me. I'd recommend starting with Stellarium.
Much of the other astro freeware is a bit too technical for those who're not deep into the hobby, but there is plenty around: astronomers are remarkably well provided!
I came across this a few weeks ago:
Celestia. An amusing package which enables you to (virtually) take a space trip around the Solar system or even around the Galaxy, if you're so minded. Not quite as polished a piece of software though, can be a bit awkward to navigate.