Just got this in email CdKeysDirect is doing a 25% off sale for steam games which means u can get:
Modern Warfare 2 steam cd key
Normally $39.17 now $29.38
Battlefield: Bad Company™ 2 Steam Edition
Normally $48.12 now $36.09
Call of Duty 4 CD-Key
Normally $22.38 now $16.78
Note: Might not work on all steam games, including the ones i listed.
BC2 is cheaper from the Steam US store. Besides, you can't activate a BC2 key on Steam.