Thanks for your note. I would suggest making a list of your top "dream" sponsors and creating targeted pitch letters to each person.
In your letter, you`ll want to include the specific benefits for each potential sponsor, testimonials from current clients/customers/partners to build credibility, media clips, and any other pertinent data that will help "sell" your business. After you send the letter, do the appropriate follow-up via phone.
People are bombarded with many messages today so you`ll want to do the pertinent research and cater your sponsor pitch to each individual organization. The personal touch will take extra time, but it will be worth the effort.