I actually use a GretaMacbeth ColorChecker 24 to be able to produce .dng and have a good color checking.
Now it is time to reach a better result, taking in to account a better calibration of the hardware involved in the entire workflow, from the camera to the printer, through the displays.
Of course there is a huge number of devices promising excellent performances, GretaMacbeth produces such devices too, but it is hard to choose the best without experience... they are quite expensive too, so the choice must be evaluated carefully :)
Any suggestion is appreciated, especially when supported by real life experiences.