If you have an Android phone or an iPhone, install Qik. It streams your video over 3G to a remote server where people can watch it in realtime, as well as gives you a remote storage of the video that the officer cannot interfere with in the event that they try to confiscate your phone (there have been plenty of cases where officers were caught destroying cell phones that people used to record video with). Qik or any similar app that will stream your video in realtime to a remote server is essential for proper police interactions.

If you're pulled over, start recording immediately. When they get to your car, ask them if they have any objections to you creating a backup video recording of your interactions to protect both yourself and the officer. If they object, fuck it, keep recording. The only reason they would object is if they're going to do something they shouldn't be doing. There's a few states where they legally can stop you, though. Check your local laws, but most states will allow you to record the event. Even if the officer says not to.