I am very happy with the Eze-fold two-sided (model 510 - medium and super fine grit, silver handle) diamond sharpener:

http://www.eze-lap.com/product/ezefold.htm

But then again, I use scandi grind knives. The wide bevel (flat area betwen the edge and the rest of the knife) makes it easy to hold the sharpener at the right angle. I've never tried to hand sharpening with other kind of grinds, but I can only guess it will be a lot harder.