Pinterest: Free
http://pinterest.com/
Pinterest can be used as a visual bookmarking site. Images from around the web can be pinned. These images can be catagorized by the author onto various bulletin or pin boards. These boards can be shared, followed and liked by other Pinterest users and are searchable.
Pearson School System (K-12) uses Pinterest for collaboration among teachers.
http://www.pearsonschoolsystems.com/blog/?p=424 f
*Pinterest requires that you request an invite.
*All images used must link back to their source.