I ran across this adorable idea by Innovative Thunder aimed at bloggers or content creators. If you'd like to offer readers/visitors a free download, do so in exchange for a tweet!
The idea is simple--rather than including the file as a plain Jane link, your reader will hit this button:
and they'll be able to download your ebook/newsletter/template file in exchange for tweeting about your free download. Once you select "Pay with a Tweet" you'll get a window that pre-formats a tweet (something like downloaded xyz from link) then you can "Post Tweet and Download Now". What an innovative marketing mix!