Good idea Tom. I have a printer that prints cards that I premake with Adobe illustrator, photoshop & fireworks.
Every customer gets a Thank You card. That is imperative.
For the houses I power wash the customers get a reminder card after 1-1/2 years or roof every 4 years, and every 6 months after that till they call me again. That is called stay-in-you-face marketing. On each card I have a spot that I had fill in with the last time I cleaned their house or roof.
Customers are amazed that I keep all of this info in an ACT database. That is imperative also. The database can be sorted any way you can imagine and you can data mine it or search for a previous customer by phone, address, name, etc.