I've found that I almost always love the Modern Warfare trailers (I say almost since I can't really recall the trailers for CoD4:MW).
That shot when you see that D.C. is a battlefield still gives me chills.
Because it worked so well here, come Black Ops, Treyarch used Emmenem (I know I'm spelling his name wrong) music for their trailers, which neither worked nor made sense since their game took place in the 60s.
Not Modern Warfare, but it's still very good. Excellent use of visuals, and that music is tippy-top.
There's also some excellent Mass Effect trailers, but I believe they've been mentioned.