If you are looking for a personal stamp (or address stamp), I wanted to recommend the seller StampOutOnline who I actually found on Etsy. I bought a custom "Mady by Mary" stamp for the back of my cards for $20. I emailed the seller and asked if she could make something with a shared M for the words made and Mary and she sent me a sample right away. I didn't like the font but loved the third one she sent me. The turn around time was amazingly fast and here is my stamp:
I have it in my hands now and it stamps well! I am so happy! Can't wait to make a new card and add this personal touch to the back.