I have used a Rayco plate in both magnetic and vacuum configurations and have not used anything better. They have a nice web site with online catalog and pricing.
they even had a CAD CD for your engineering people to draw up for inspection and setup instructions.
Ask for Larry or Debbie, tell them I referred you, and they will give you very good service. I have Known Larry for about 4-5 years and he will take care of all your work holding needs if possible.

Duane Wade