I found curriki.org (curriculum wiki) via Joyce Valenza's Twitter Page and shot it out to about a half dozen other teachers almost immediately. This is an open source wiki dedicated to providing free lessons, units, even whole courses to anybody who wants to use them. The lessons and units seem fairly thorough, but it's not quite as complete as I'd like it to be...yet.
Give it time. As more people become aware of it and start utilizing it, it will no doubt become a major resource.