Auxiliary Lighting
This is split into 3 categories, fog lights, Auxiliary Low, and driving lights. There is a test winner in each category.
Fog lights
First of all, fog lights works best in fog or low visibility, with headlamps turned off and at speeds below ~70km/h (equals to 50mph). They lit up the road relatively close (30meters) to the car, spreading from far left, to far right, at relatively low max. brightness. By having a low cutoff, and a low mounting point, glare from the fog will not be reflected back to the drivers eyes, which typically headlamps do. Authorities requirements for fog lights are very general, so be ready to see a lot of variations out there. There is many OEM applications where you are not able to turn fog lamps on without having headlamps on. This is what I would call cosmetic fogligths.
Most people don't need fog lights because it very seldom fog appears unless you are close to the ocean or great lakes. But hey, it looks cool, nicely inserted underneath the bumper. From time to time, car magazines and car shows presentes several cars that have replaced headlamps with fog lamps. This is not a good solution. Its dangerous at highway speeds. A typical fog lamp doesn't have the enough brightness down the road. Some HID fog lights have shown up on the marked around year 2000. Nothing wrong with using HID, but its a waste of money. HID usually means brighter output, and that is defiantly something you do not want in fog light. A too bright fog lamp used in fog will only lit up the fog better, increasing the "wall" effect of fog, and make the road less visible. I would suggest to usage of a 10 or 18W HID system instead. They are available in flash lights for divers. See:
http://www.extreme-exposure.com/. In comparison to well known D2* HID lamps, these lower power HID lamps is still in the stone age. They take a few minutes to start up, they are very costly.