Which books should be read as important for good playing ?

I have diligently been reading the "Mathematics Of Poker (Bill Chen)", not only to improve my abilities, also as hobby because I simply love mathematics. It makes the game more interesting for me, makes me think. Perhaps, it is not enough.
So, what kind of "poker" books do you advise ?

The books that are most appropriate for you depend on such factors as your ability level, the type(s) of poker that interest you, and the level at which you play.