The Student Room Group
You could try some of his French predecessors like Camus or Sartre who are both, at times, darkly humorous (although lack some of the profanity Houellebecq seems to have mastered). Again, slightly more subtle, you could read some Kafka which also dark and funny. If it's not subtlety you're after (which is entirely possible!) then maybe American Psycho by Bret Easton Ellis? It's contemporary and almost as much an assault on the senses as Atomised was (I haven't read Platform). In a vaguely similar satirical and heavy-hitting vein you could read Fight Club or A Clockwork Orange (I haven't read the former, but the film's great and I've heard good things about the book from a friend). Also, I expect you're aware of this, but there's a newish Houellebecq called The Possibility of an Island.