I downloaded a new photo app for the iPhone this morning, and its a lot of fun: Hipstamatic. Its meant to emulate an old plastic toy camera. You get a choice of three lenses, three film types (affects the frame of the picture) and two flashes for the 1.99 app download. You can also buy more lenses, films, and flashes from the Hipstamatic Mart. I haven't bought anything from the mart yet, but I probably will in the future. Its very easy to take pics straight from the app and upload to Flickr (as I have with the ones below) or to post to Facebook. My only complaint is that there's no option to tweet your photos, or if there is, they've made the option too difficult to find.
I had some fun switching lenses and photographing the same Coke bottle on my desk: