Saw a great example of how to thank golf tournament sponsors today. A volunteer went from hole to hole and took digital pictures of each team, each individual, and each sign on a hole indicating the sponsor. Following the event, the pictures were put on card stock - and each sponsor got a picture of the team sponsored or hole sponsored; and each player got a picture too. On the reverse was a thank you note, info about total raised, and how it was being used. This was put in an envelope, but might be easy to produce as a postcard too.
Really inexpensive but personalized way to say thank you to sponsors.