What is the best cpu below $200 fro gaming like call of duty mw2 ,mw3 and stuf

de5_roy had the most complete answer, but I'd just like to point out that the i3 2120 can be had for nearly the same exact price as the 2100, so I'd get that for the free 200Mhz bump in speed. I build a $600 system a few months ago and went with the i3 2120 and it runs like a champ.
 
i5-2400 since I've read that MMO games like BF3 can use more than two cores. Don't know about MW3.

Most games only use 2 cores. But games that can use more than 3 cores are slowly creeping up, however, they will still be the minority even 5 years from now because the more cores used to more time and money needs to be spent on development.
 
amd fx 4100+asusm5a88-14 , will cost u around $200 . good value for money cpu combination , you can also add a ati radeon hd 6670 1gb ddr5 graphic card to take cares of call of duty game .0r you can go for a same configuration in intel if you are an intel fan by getting a core i3 2100 + an intel board in the same budget also with an ati raeon hd 6670 included but for an additional $80.
 
for those games a i3-2100, phenom2 980, a8-3870k is also good.
mw2,mw3 use very little cpu+gpu power at extra settings at 1920x1200 (filltering off).
But you have budget around 200 then i5-2550k is a good option to consider for all future games.

To get 75fps at those settings, atleast a 6770 is required.
Which gpu you have/planning?
 
i think the thread is going off topic.
OP: for gfx card query, ask in that section. for opinions on full system, ask in the system section. you'll get better help in the appropriate sections.
core i3 or core i5 2xxx cpus can handle from entry level to high end cards with ease, they will run currently available gfx cards fine.