Yahoo is building a combination of social network, collaborative space and (most of all), lesson plan creator for educators called Yahoo Teachers.
The first part of the site is the "Gobbler" - a browser add-on that helps teachers save photos, text and sites from around the web in one place (see this video). Once Gobbled, users move to the second stage: organizing that information into lesson plans and worksheets, tagging them and sharing them with others to save time.
This one is sure to be a hit with teachers, adding so much more efficiency to lesson plan creation. The project is still under development, but coming along nicely. Teachers can enter an email address for an invite.