Certificates and thank you are easy if you use the mail merge in Microsoft Word. We keep a database of what everyone donates and then merge it into a thank you letter along with the contact person. The next year, we again use mail merge to remind what they gave this year, and ask for them to again help us out. My assistant makes it look easy and says anyone with working knowledge of Word can use mail merge.
I send both a letter and a certificate. Certificates are easy since you only need to fill in the business name. I think local businesses like to post them. After-all, among the many reasons a business donated in the first place is the fact that they are hoping for some free advertinsing! Doesn't take long to do and I hope that they remember us for hte next time we might ask!
I was planning on handwriting thank you notes. However, I noticed a local business had a framed certificate displayed thanking them for participating in another school's auction. Do you think the certificates would be preferred for that reason?