You should be able to find plenty of camera choices if you go to any car audio/video install shop, or just do more search on the net.
I didn't put too much thought into camera when I was getting it, I was mostly concerned with the monitor.
Just did a qucik search on the model number of the camera I have, and found the manufacturer's site.
Here's a page with a few of them, mine is Model No JPC-3800P.
http://www.jjcomm.com/product/internet.htm

Pretty much any camera of that size is quite easy to install. Japanese spec VX which was produced before the american one, had a camera as standard equipment, so there's a space for it in the rear door. You can see what will fit if you take off the "half moon" plastic. And, as you can see, there's a "slot" for the camera in the plastic itself, just take out the stub that's in there now. The only "custom work" I had the install guys do was to put the clear plastic in that "slot" to cover the camera. This is optonal tough: many cameras are wateproof and the half moon provides enough protecton as is.

I'll post pictures of my install within the next few weeks.

hope it helps,
- Ed Y.