Good books on automata theory?

I asked “What is a good book on automata theory?” because I don’t recall much of it from college. Marco replied here: Elements of the Theory of Computation by Lewis and Papadimitriou.
Do you know of any more?
Addendum: 19/02/09
Prabhakar added:

The 1979 edition of “Introduction to Automata Theory, Languages, and Computation“, by Hopcroft and Ullman. The algorithms are pretty imperative, though.

Addendum: 20/02/09 at 2:25CST
Jos added:

I very much appreciate: Formal Languages and their |Relation to Automata by John E. Hopcroft and Jeffrey D. Ullman. My first read through it was 40 years ago, but even nowadays I consult it now and then.