BrainPopJr. had some great videos to get students started on their topics.
I also saw a game on Technology Rocks. Seriously's blog that the kids loved, from Compass Learning. Very cute!
And finally, this is a generator from the University of Texas that shows kids how much they would weigh on the Earth vs. the Moon.
The project students have been working on is a KidPix slideshow. Students are making slides for the Sun, Moon, and Stars, including detailed pictures and facts they have learned. Then we are putting the slides together and making a QuickTime movie. I think it will be a great finished project!