Daniel Negreanu, Phil Helmuth, Doyle Brunson, Gus Hansen, Dan Harrington, Jonathan Little, David Sklansky, Phil Gordon... Almost all of them are already mentioned here so here's another vote for them! I have books from everyone of them and I have learned something new from every book. Everything they teach doesn't fit into my own style but that doesn't matter, its' still knowledge.
There are so many
poker books in the world that it's not a miracle that some of them might not be good. One good rule is to make your own background check for each author and Google their name to see what they have accomplished in their career, read reviews about their books and then decide if the book might be worth reading or not.