Curriki is an online [wiki-based] community and wiki platform for teachers, learners, and education experts to share, reuse, and remix quality curricula. This is an extensive and popular repository, through which teachers can find and develop resources, share lesson plans, and collaborate on courses with others in their school or around the world. All content is OER available under CC-BY.
Curriki is now an international community, but key players are still mainly US-based (as are board members).
Curriki is the result of work done for GELC - the Global Education and Learning Community - an online project started by Sun Microsystems to develop works for education in a collaborative effort.