The Nikon 24 PC-E is for sure nice, but I have to admit to a bit of Canon envy in this regard. Not only does Canon give you independent tilt/shift controls, but the image circle seems to be a bit bigger (and a bit better at the edges).
I'm not sure that I agree the 24 PC-E's distortion is easily corrected. Using PTLens can help automate the process some (not as much as I'd like), but it still requires recording the amount of shift used for each shot taken. Not a big deal if you're primarily using the shift for stitching, since the shift amount will probably always be the same. But if you're shifting for compositional reasons, you could be using anything from a few mm to 10 or 11mm; and you need to know that to be able to correct the distortion. I really need to get better at remembering to the voice-memo on my camera.