Oh, yeah. (showing my age) I remember when games didn't get "trailers". You either read about them in game mags and that was about it. On occasion, they would do a tv commercial. Anywho...
CoD: Modern Warfare
Didn't go out and buy it after seeing the trailer, but it was very impressive. More so when they said it was in game footage.
Diablo 2 TV Commercial
This is the first TV commercial that I recall. I'm sure there were others before, but this one stands out for me. Mainly because I was playing it at the time.

Still am.
Sure I'll remember more later.
Oh! Errr... How could I forget these. Just going to post the main page, WAY to many to post for one game. And expansions.
Fallout 3