There is already socialcoder for non profits, which also provides project management and liaison. This thread would not do better than that service for non-profits, simply because it's more organized.
That service does a lot of the matching that you need and provides all roles from PM to designers to programmers. It's unquestionably better as you're dealing with volunteers. Unless you're picky with who you select and then lucky for them to have enough continued time for you.
Companies just want a resume and straight to interviews.
