Are you looking for accurate gears or "eye candy" gears?
Alibrescript has a few gear functions which seem to be reasonably accurate.
Utilities for Alibre by David Bolsover creates quite accurate gears (search for them here)
I have a script that builds an eye candy tooth. I create the gear blank and run the script to create a tooth which I then have to pattern. (maybe one day circular patterns will be added to scripting)
I work in a gear shop so all our gears are hobbed, not milled, so the model only needs to be accurate for the turning blank. The drawings look pretty good though.