Last year, I stumbled across an iOS app called PhotoCard, by Bill Atkinson. This app allows you to create free, electronic postcards from your iOS photos, personalize them, and send them via email.
You can also convert your postcards into gorgeous physical postcards and mail them to other people. That, of course, is not free but it is also very reasonably priced. I've sent quite a few of them and they are beautiful and very noteworthy, since they are 8.25 x 5.5 inch cards printed in high-quality color printing and mailed by US Mail.
Editing a picture I snapped of The Gherkin tower in London, which I sent as a postcard.
The app comes with over 200 of Bill's own photos, so you can compose something beautiful, or you can use your favorite snaps from your camera roll or photostream.
You create both the front and the back of the card, including your message and the style of the stamp if you are sending physical cards.
If you want to stand out from the crowd, this is a great way to do it. I love this app.