[groovy2shoes]

The Sipser book is excellent. It's one of only a handful of textbooks I decided to keep after I graduated from university. And perhaps the only one I kept because of how good it was rather than because the campus bookstore wanted to give me a pittance for it... and I didn't even buy the book until after the semester when I had to return the copy I'd checked out from the library...

I later on picked up the first two editions of Hopcroft & Ullman for $1 each at a used book store. I don't think either edition can really hold a candle to the Sipser book, which is shorter, more thorough, and (imo) easier to understand.

One caveat: it's super-expensive. I'd recommend finding a used copy or even an "international edition" (which will be soft-cover rather than hard-cover, but the content is the same).