Memplai is a cool new (beta) site for creating collaborative videos that I just found out about from Larry Ferlazzo's blog. These videos are easy to create and a user can upload any video or photo to include in their project. Also, a user can invite others from their social networks to contribute content to a video and then share the final project.
I highly recommend checking out Memplai by clicking here!!
For my top 10 sites for creating/editing video click here. FYI, Jaycut is no longer in service.