OSM Tasking Manager - allows a group of mappers to coordinate and divide up mapping tasks geographically.

Through this I discovered…

Humanitarian OpenStreetMap Team - OSM for a cause! You need nothing more than Potlatch to make a difference.

And through that I discovered…

Walking Papers - Offline and portable OSM mapping still kinda sucks, so Walking Papers allows printing sections of OSM on paper, then scanning your notes back in to work with them online.