I have got many good ideas from all of you and have not been in this long enough to give much back. One good seller I have found is for reproduction pilot certificates (US). Take a sample into your airport FBO pilot shop or post something on the bulletin board of smaller airports.
I have got great response with this, engraving it on marble, wood and Romark. Remind the buyer that the certificate number is their SSN, so they might want to put a ficticious number on it if they plan to hang it in a public area. Pilots with several ratings will have to settle for the ratings they want to display (multiple ratings are on the back of the certificate).