Like rvcahawaii808 mentioned, I run PIAA ions and atps on my light bar. The combo does very well in all conditions. However, my ion's are driving and not fog. I have 3000k HID in my stock fogs so i rely on those as well as my ions to cut through fog and rain.
When it comes to light choices, you can't really go wrong with the major brands like Lightforce, PIAA or Hellas (there may be more but these are the ones i've seen in person). If you like the slimmer look, go with Piaa's or Hella's. If that's not a concern, then take a look at a set of Lightforces.
PIAA
Pros:
very bright
on the slim size from a profile standpoint
available on the net for a cheap price
Buy a specific color at the same price - no additional filter needed
Cons:
Glass lens (replacements are expensive)
Lightforce
Pros:
very bright
swap out lenses depending on conditions
bulletproof casing (literally)
Change the beam pattern like a mag light from pencil to dispersion
Cons:
on the higher end of the scale on price
takes up more space due to design
One flavor only - you have to buy a filter for different colors
Good luck
Kevin