RSS's multi-mumbple pro pano whatever that neuro mentions is an awesome piece of kit. It takes a bit of fiddling to get everything lined up...but, once you do, you've got the equivalent of a giant virtual lens. You can point it in any direction without any parallax problems at all.
But, unless you need really, really big panoramas, you might also want to consider nothing more than a Shorty McForty without any special panning heads. The nodal point is so close to the focal plane that you only have practical parallax problems if you're including stuff right in front of the camera in the shot -- not something one typically does with panoramas. Put it in portrait orientation (with your L-bracket), make sure your tripod is level, and you've got a most awesome pano setup right there. With that setup on a 5DIII, you can do a two-foot-high by however-wide print of your panorama at 240 ppi. Even if you've got a printer that'll print wider, dealing with that much paper in a single print is something of a hassle....