Free GM Resource: Gridzzly
Gridzzly is quite easy to use. Select one of six basic types (3 dotted, one lined, and two basic shapes....square or hex) and move a slider left to right to change the size. Print and you are done!
There is a ruler of sorts across the top of the screen for trying to size out the graph paper, it isn't marked in either numbers or even system, so I'm not sure if the largest hexes are measured in mm or inches.
If you can get past the issues with trying to make a specific size graph paper, probably a minor issue for many, then you might get a lot of use out of Gridzzly.