There's a teaser site that's gone live with an image consisting of a frame from the teaser trailer and nothing else. The domain name is 1-18-08.com, presumably referring to the movie's release date.
The teaser was attached to Transformers and I have to admit it looked pretty cool. I haven't really followed all the rumours and spy stuff on this movie, but I liked the trailer. It had a very "real" feeling about it that was very effective. It looks like it's some kind of giant monster/alien movie and I've heard speculation that it might be an American version of the Korean film The Host, but as I said, that's pure speculation.
[UPDATE: Here's a look at the brand new Quicktime trailer:]
For larger versions of the trailer go here (Thanks, Paul!).