Though he is most famous for Fight Club (largely due to the film) he has a lot more to offer than that. His current trilogy, Damned, Doomed and an as yet unreleased book, is a hilarious look at religion and celebrity culture. It's a perfect blend of his ability to be repulsive and hilariously ridiculous. He writes about a religion based around profanity and describes hell as having rivers of vomit.
He can blend perfectly believable characters with people who are so ridiculous that they can't possibly exist and although he keeps himself grounded in the real world he manages to fill it with things that you know would never happen and make it hilarious.
Through Choke and Survivor he tears into the ideas of sex and religion and through Invisible Monsters he tackles beauty. His books are serious and satirical but he keeps them fast paced and funny. His style isn't exactly flowery, his description is vivid but quite minimal and he writes in such a way that things are always moving forward, and fast.
If you've never read any of his stuff then start with Fight Club, I don't think it's his best but it's his first one and is probably his most accessible. Afterwards Choke, Survivor and Invisible Monsters are all essential and for some of his latest work I'd recommend Damned. His newest book is Beautiful You is out but I can't recommend that just yet because I haven't read it.