Soundation is a powerful online music studio with recordings, effects, virtual instruments and over 400 free loops and sounds. This is another great option for those student more interested in the audio side of video production.
Geared more towards high school students, but could possibly be used in lower grades with a small amount of training.
This website is different than many that I have come across. It allows the user to choose characters, backgrounds, etc. and the dialogue. The website then takes the text and matches it up with the cartoonish characters mouth and creates a movie for you. This could be a great option for classrooms that do have the budget for digital cameras.
This could be used in any grade level. however a greater amount of training would be required for younger grade levels.