I've created a lot of 3D printed gears over the last few years and one of the best tools I've found is from Rainer Hessmer.

http://hessmer.org/gears/InvoluteSpurGearBuilder.html

It allows you to specify additional parameters like backlash, clearance, and profile shift. It also allows you to output in DXF which tends to be more of a standard in the engineering world.