The Gears' 1-3 ones always stick with me. Even the 4th one I hadn't seen and that looks alright anyway.
The Borderlands' original trailer was pretty lackluster - 3 years later they sold it's sequel with a lot more of it's strengths;
Destroy All Humans had a few, but this is the one that sold me it as a kid;
Halo has some damn good live action trailers. The Halo 3 ones should be up here too, but this was the first one I saw on TV;
Deus Ex doesn't show much gameplay though it does have a very good way of displaying the features through the trailers,and even a large part of the story without ultimately spoiling anything. The monologue reads out a bit like a techno version of Hatred
And further onto the topic of dystopian alternative futures (...right?), there's Fallout 3 with a general "everything's fucked" tone;
to NV's "Well, everything's not all bad, we have casinos..."
to 4's "Yep, still fucked"
Then we have the
Russian take on the upcoming apocalypse; less 50's idealistic superficial coating over a dystopia, just straight up hellish with a hint of slightly different make-believe;
So yeah, that last one is out next year and it's been the only new game series I've pre-ordered, and the only one I'm ordering for next year methinks.