How do you thank your customers for their business?

I'm reading The Business of Consulting by Elaine Biech. She suggests sending handwritten thank you notes and creative gifts to customers to thank them for their business and keep you top of mind. So it got me thinking...How do other PSO managers thank their customers? If you are doing anything unique, funny, or generally effective in reinforcing your team's value proposition, please share. We'll all benefit. Thanks in advance.