I have been through a slew of logic texts. By far, my favorite for both theory and practice is Computability and Logic by Boolos, Burgess and Jeffrey.

http://www.amazon.com/Computability-Logic-George-S-Boolos/dp...

Another very good book on nuts and bolts proofs in both propositional and predicate logic is Beginning Logic by E. J. Lemmon.

http://www.amazon.com/Beginning-Logic-E-J-Lemmon/dp/09151445...

And a great collection of primary texts covering the history of modern logic is From Frege to Godel..., edited by Jean van Heijenoort.

http://www.amazon.com/Frege-Godel-Mathematical-1879-1931-Sci...