I put HIDs into my reverse lights. You can't get any brighter than that. The only problem is that the HIDs take a while to warm up and get brighter, so I used the HID low with halogen high bulb (9007), and modified it to fit in the reverse light hole. Using a relay and switch, I am able to just put it in reverse, and have the halogen bulb instantly come on, and if I need extra light, I flick a switch in my armrest and turn on the HID bulb as well.
This is also good for tailgaters... LOL
Holy fock, even I never tried this. I gotta see pics man.