Logics

I've found this book to provide a clear and enjoyable introduction to formal logic. Mark Sainsbury's Logical Forms, which deals with philosophical aspects of logic, complements it nicely.

The best book I've seen on formal logic(s) in a while; it covers almost every type of logic the advanced undergrad might want: modal, intuitionist, etc., in addition to propositional & predicate, of course. I would read this along with Philosophy of Logics (Haack); apart from the fact that since Haack is a semantic or philosophical look at the formal systems of logic, you get a more rounded view on logics, both of them have in common a 'pluralistic' attitude to logic, hence the 'logics' in both books.

This book is simply great! It covers a lot of stuff in a friendly manner, but without being shallow. Its semantic approach to logic and its clear treatment of metatheory are, in my view, the main assets of this book. Buy it!