If you haven't yet, check out iTunes U. There are lots of free science courses available there. Here is one I found:
Survey of Astronomy from Missouri State University
Also check out the Apple apps. I also downloaded a free iPhone/iPod Touch app for my daughters to quiz them on their Greek alphabet.
Lots in the Apple store to explore. Happy hunting.
P.S. Big thanks to my husband for remaking my blog banner. I think it looks great.