I have read the Hobbit many, many times, it seems that book never gets old to me.
I have also read the Fellowship of the Ring many, many times.
I have also read Return of the King many, many times.
However, I always find myself skipping over The Two Towers once I get to a certain point, the same thing happened to me when I read the Lord of the Rings the first time, but I soon picked back up on it.
I probably have only read the Two Towers about two or three times. Shame, shame, I know.
EDIT: Oh, almost forgot. The Silmarillion! I have read it about... once, though I often go back to it and read certain parts over again for reference.