Funny story about Donnie Darko: Mrs. Lemur and I were on a kick watching old noir films, skimming through the classics for about a month. On an impulse I grabbed Donnie Darko, which we watched as soon as we were done with Night of the Hunter. As soon as Donnie Darko finished, Mrs. Lemur turned to me and exclaimed, "I can't believe that was good and new!"

Personally I'd recommend watching the original cut, not the Director's Version or whatever.

I'll second Shaun of the Dead, which I thought was actually funnier than Hot Fuzz, but that may just be my Yank sensibilities.

Cloverfield is definitely worth a rental. First film where they were confident enough in the digital effects to backpedal them.

Might want to try The Descent as well. Exceptionally well-crafted indie horror flick by the same director who made Dog Soldiers. (He also made the more recent Doomsday, but that film is just too darn silly for its own good.)

Ever seen The Thing? It's a horror classic from the 1980s.

Children of Men is worth your time. Very adult SF film.

You know what, maybe if you could tell us a few more films that you like, we might be able to give you better advice ...