I was working on integrating a custom iframe tab in a Facebook app, and was having a lot of trouble displaying it to users browsing FB with SSL enabled. I don't have a server with an SSL certificate, and didn't want to pay for a new host or bother with getting a certificate.
You know who does have an SSL certificate? Dropbox. It's certainly a hack, but you can serve the iframe document from your public folder, and it works really well. There are bandwidth caps (10GB/day unpaid, 250GB/day paid - https://www.dropbox.com/help/45), but it could be a great solution for some situations.