warmwxrules: I would not recommend using any fiberglass in a basement due to the potential for condensation (unless your foundation happens to be insulated already on the exterior). Also, insulation needs to be in contact with the surface it's insulating so leaving a gap will not result in good performance. Rigid foam is the way to go and it's really not necessary to construct full stud walls either. Here's a diagram I send out to my clients on a good way to insulate basements:
https://docs.google.com/open?id=0BxW...thkey=CMXjveQJ
This is relevant to the rim joist discussion because when you spray foam that area you can bring it down on top of the rigid foam and form a nice continuous layer of insulation.