I really like FotoFlexer because I can see it easily used in a classroom. What a fun way for students to be able to edit and experience photos in a new way! Students can use this website on projects and teachers can use it as a different form of assessment. Great for visual learners!
Netflix is one of my personal favorite websites. There are so many videos and TV episodes available instantly and through the mail. This would be a great way to harness everything that the history and discovery channel offers!
For a complete list of great resources check out the 100 Best Web 2.0 Classroom Tools!