Jamendo is a bit of a mess; users upload their material (of wildly varying musical quality) and the one keyword at a time searching makes finding anything worthwhile really quite tedious. However, anything found here can be used for non-profit projects at no cost at all.
Magnatune is a much classier operation. The music is hand-selected and sorted sensibly into meaningful genres. For non-profit use, tracks can be used under CC terms for merely the cost of downloading the tracks (min $5.00 per album). The best thing here is that the tracks are also available for profit-making production work too under numerous types of licensing agreements. This is a very open and scalable solution; a project could start out on a non-profit basis but further licenses are obtainable should the need arise.