Vuvox is a new (beta) site I just heard about from Free Technology 4 Teachers. There are lots of sites that let you create a slide show/presentation, but Vuvox may be one of the nicest.
First off, Vuvox has a really nice/sleek look to it. You can build some really nice presentations that includes video, photos, and audio. Also, you have the ability to create a collage or an "express" video which is fast and easy. Finally, Vuvox has some really nice video tutorials on their site which help the user learn how to use their program.
I did look at their acceptable use policy, and it is pretty standard. Any obscene/inappropriate material the user will be removed and can face subsequent punishment. However, I don't believe they have any filtering/moderating policies so it might not be ideal for student use.
Give Vuvox a look by clicking here.