I just found about these recently:
www.earvana.com
Compensated nut, instead of just the saddle.
Haven't tried them yet but I am going to. Others I have talked to bought one to try, then bought them for every guitar they owned. Seems like a good idea.
Click on the "Technology" tab to see the pitch variations. Different than Buzz Feiten, the Earvana looks to work on every string, all the way up the neck.
Steve