I think UbiSoft have always done a great job with trailers, especially the Assassins games. I preferred this one from AC3
http://www.youtube.com/watch?v=pAb-Joqhrz8
Every element is spot on; music, editing and amount of gameplay shown. Admittedly, the CG trailer from E3 kinda promised too much, but this trailer was a great way to show off the game. However, I've seen some great fan-made trailers. These two are my picks:
http://www.youtube.com/watch?v=DogoEY6v-vA
Did a much better job than Dice in making me interested in the game, and yes I know the song is the same, what can I say, I like the song and it works well in trailers.
http://www.youtube.com/watch?v=ANjS1osIid4
This guy is amazing when it comes to fan trailers. Seriously, go look him up on YouTube, he's awesome. Admittedly, Mass Effect has lot of good trailer material, but these five minutes could have been used in the actual marketing for the game.