It's no secret that I'm in love with the Hipstamatic app for the iPhone. It's one of my favorite apps because it has such a vintage feel and a retro vibe. It's downright funky in fact, though some may find it over the top for their tastes. While many opt to use the Hipsta (as I call it) right out of the camera, I often combine it with other applications to help me get the exact look I want. Adjusting contrast and color can be done in Best Camera, for example, and you can combine it with Shake It Polaroid to get an ultra hip totally square retro cool JPEG of goodness.
The popular website Photojojo did an ultimate Hipstamatic guide of sorts, you can find that here.
The Hipstamatic app is really one fine app, and it's a must to download if you do not have it already.