Here are some great free sites designed to be used in K12 education. Safe for K12 student use (no "wardrobe malfunctions") and judged to have educational value. Some provide a free place for you to post student work for a worldwide viewing audience, without the problems of YouTube.
SchoolTube.com - student/teacher made videos, previewed for educational appropriateness
eSchoolnews.tv- student-made videos, also interviews at major education and ed tech conferences with keynote speakers and other leaders. Lots of great things for both students and teachers to watch
TeacherTube.com - videos, audio files, digital files, photos, teaching resources, all appropriate for K12 use
ePals.com - largest and fastest growing online K12 community, in 200 countries, 700,000 teachers, 27 million users monthly.
Student Media Galleries - K12 student digital work including PPT, PDF, photos, videos, scanned images, in English and other languages. Quite a few posted from girls HS in Cairo just before and after revolution. 17 videos from school in Senegal with no electricity. Lots of digital stories created by students in US and other countries too.
PBL to collaborate with other K12 classrooms online - in English and some in Spanish too!
Eduteka- great site, all in Spanish from Cali, Colombia, about using ICT in K12 Spanish-speaking classrooms
A great list, Med, and I also love the suggestions shared here by others.
I'd add Testmoz, an incredibly easy, free, self-checking online quiz generator. You can read about it here to decide if it's the right tool for you; I shared strengths and possible pitfalls which will help you decide.
To enjoy all the benefits of video sharing and utilizing video in the classroom to the fullest, you need to check out SchoolTube.com. It is a safe, FREE video sharing website exclusively approved by over a dozen National Education Associations for use in K-12 schools. Educators and students can enjoy a safe and fun video sharing environment to enhance their classrooms and learning experiences. All student videos uploaded must be approved by educators before going live. This produces a refreshing site that is appopriate for school use and gets both educators and student involved in digital learning.
Also SchoolTube hosts a variety of on-line video contests that both students and teachers find a great value and fun in participating in! With over 20 Categories of types of videos surely you will find many you would like to share. Here is just one example from the Science Category. Enjoy.....