Well you asked for the best laptop and here it comes :
Progress UXG i7920N Faith Japan's First Core i7 Extreme Edition with 3 SSD Notebook : Akihabara News .com
Core i7 965, GTX 280 :P - but I wouldn't even call it a laptop since the weight is around 11 pounds and the batteri time is properly....
But well to the serios part. I must admit that I don't know the exact system requirement for COD but I suppose thats its around the same as L4D. It is not a question about what brand you are buying, a HP can easely be good for gaming. But where most laptops fail is the GPU!!!! You must make sure that you get one with 512 MB DEDICATED ram, this can be either nvidia 9xxx or Ati 4xxx that you would head for.
As for the cpu you will need to head for a dualcore atleast on around 2,2 gch as a minimum! I Would suggest a bit more if your going for amd, and if its going to play games in the future (l4d 2 might require more) then would I head for a 2,4 gch + dualcore atleast or maybe a quadcore.
About the ram you will want atleast 2gb if your running xp and 4gb if your running vista. With windows 7 3gb should be enough, ( 3 gb would maybe also be enough on vista). As a last thing when your speaking about running games this is the priority you should make : gpu>cpu>ram>rest.
Hope this helps or else I Will have to link to some danish sites lol:D
But feel free to post a link to a specific computer and I will check it out.