Not really a trailer (although I think there's a version that's edited together with the actual trailer), but I love the promo for Face/Off where it's John Travolta's character talking about Nicolas Cage's character as the camera slowly pans around him... then after it's done a full 360, we see that Travolta is now Nic Cage.

While it did mislead me into thinking Face/Off would be even more out there than it already was, I still think about that trailer/promo/whatever often. Blew my little kid mind, back in the day.