The two most recognizable voices in the world of movie trailers today are Don LaFontaine and Hal Douglas. There are other guys who narrate movie trailers but a majority of them are "doing" LaFontaine or Douglas, at least to some extent. There are also other voiceover guys who profess to be combining the two.
LaFontaine is the guy you associate with Arnold Schwarzenegger and the Terminator II commercials. Here's a link to a demo of his work, and you'll need the dreaded RealPlayer installed to hear it.
And you can not only hear Hal Douglas but actually see him at work. He's on-camera for the trailer for the Jerry Seinfeld documentary, Comedian. Here's a link to a site where — assuming you have Apple QuickTime installed — you can view said trailer, which is very funny. (Thanks to Marc Wielage for the referral.)