If you are a looking for a fun way to send correspondence, check out the Bureau of Communications. They provide a free service that creates all sorts of correspondence using a Mad-libs-type format. They have forms available for holiday observances, apologies, thanks yous, airing grievances, invitations, and more. You just fill out the form and they create a nice, pseudo-official, but obviously fake, looking form for you. Just the thing for some people.

An example of a thank you letter.