So almost everyone here has named directors of popular action and sci-fi movies (James Cameron, Joss Whedon, Martin Scorsese, etc.). Tarantino almost always makes the list as well.
I like all these guys (although I take Whedon with a grain of salt), but I prefer some of the lesser worshiped directors.
David Fincher...probably the most well-known on the list, but his movies are almost always amazing...Panic Room, Fight Club, Zodiac, The Curious Case of Benjamin's Butt, Se7en...
Cameron Crowe...going to get called gay for this, but I've come to like him after seeing Jerry Maguire and Vanilla Sky.
Michael Mann...Heat and Collateral were freaking amazing, as was The Insider. Miami Vice is probably his only "ehhh..." movie I've seen.
The Coen brothers...I've liked everything I've seen by them so far except A Serious Man, and even that had its moments.