Here are 4 fun camera apps for the iPhone. I use them all. I like adding different effects to photos. This one is XnSketch. I think I've blogged about it before.
This one is Vintique. One of may possible filters. All of these little apps have many, many filters. Lots of ways to spend time while in the car.
Here is ClassicINSTA. I like using the same photo in many apps to see what I get. Some photos work better in some apps than others.
For a little retro fun here is XnRetro. Enjoy!