I have the BMW system cases and a Cortech Super Mini tank bag:
http://tourmaster.com/xcart/product.php?productid=142&cat=31
I hated the BMW tank bag. I think tank bags - like all luggage - should never get in the way. The BMW bag got in the way. It prevented me from leaning forward into any sort of aggressive riding position.
I tossed my EZPass in the top clear vinyl part of the tank bag (since I have a GPS anyway); it works great. The Cortech bag also has a hole for helmet comms/radio/etc, and costs about $50.