I'm pretty much an expert at this.
Best option by far is a color bullet cam with 480 TVL or higher, with an external mike, fed into a miniDV camcorder that has a "video in" port. You want to get a large fanny pack, pad the camcorder with a lot of closed cell foam like Funnoodle, and turn the pack so the camera is in the small of your back. You need a 9v battery for the camera and its mikes though.
Put the bullet camera on a headband. There is a type of headband used to hold a flashlight that will do very nicely though you will need to do some adjustment as it points the camera way too high. The headband mount is essential. Put it on a gun and the camera bobs everywhere and the footage causes major motion sickness and has few usable frames. The head, on the other hand, natually has very effective stabilizing effects. You can learn to hold your head a bit differently as you walk and scan back and forth with your eyes while keeping the head cam on one target for a moment.
There is also a small memory-card driven digital bullet camera. Customer reviews and footage examples show it's not nearly as good a quality. Somewhat disappointing, actally.