I think the theory of poker is regarded as a must-read for ring games though (cash games). Personally I regard it as such...
Limit/NL or doesn't matter? I play NL, and was going to buy that book last night but they didn't have it at Borders. But maybe I should still get it?
Right now, I'm reading through Gordon's Little Green Book(read some of the little black book, but skipped past a lot) and have the Little Blue Book on deck. I have Hilger's Texas Hold'em
odds and Probabilities too, but I haven't read it much.