If you are in the mood for something advanced, take a look at Introduction to Automata Theory, Languages, and Computation by Hopcroft, Motwani, and Ullman. It

If you are in the mood for something advanced, take a look at Introduction to Automata Theory, Languages, and Computation by Hopcroft, Motwani, and Ullman. It has a good amount of proofs and a pretty strong focus on automata thought so that may not be your cup of tea. Hopcroft won the Turing award in 1986 so he knows what he's talking about.