I really don't think there's an equivalent of Animal Liberation on the other side. That's a classic because it's very clear and philosophically acute, very accessible to the public, full of information, and broad in scope. There are books on the other side, but they tend not to have all those virtues. The book that Amy Kind suggests is a good option, though it's mainly about animal experimentation, not meat-eating. Another book on the other side is The Animals Issue, by Peter Carruthers. It's clearly written and some would say acute, but it's primarily oriented to the academic philosopher. It's nowhere near as readable as Animal Liberation and it's not a source for "real world" information about the treatment of animals. Carruthers wouldn't be interested in such things, since he argues animals don't suffer at our hands--they're not even conscious, on his view.

A very accessible and pretty interesting book on the other side by a non-philosopher is Covenant of the Wild: Why Animals Chose Domestication by Stephen Budiansky. If you don't insist on a position diametrically opposed to Singer's, then another book that defends meat eating is The Omnivore's Dilemma, by Michael Pollan. Not a philosopher, but a clear thinker with a good grip on the animal ethics literature, he defends consuming meat produced on tiny humane farms, while excoriating modern industrial agriculture.