Rockler makes a dovetail jig.
http://www.rockler.com/woodworking-jigs/joinery-jigs/dovetail-jigs?sid=v9105&gclid=CIr09pCShMECFTOZMgodn0gA6Q 

How does it compare to the Porter Cable jig 12" model.

I don't make a lot of dovetails but I have $29 Harbor Freight jig that I've made work.  It's a pain though.  And FORGET cutting them by hand, I need a jig to make a jig, I have no ability to hand cut dovetail.

This is one that I did.

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