I recently finished teaching Peter Singer's Animal Liberation to my The Animal and the Ethical class. I hadn't read this book since I was an undergrad (not that long ago, but still, long enough), and I was amazed as I taught how much I generally liked the book. I didn't particularly care for the book when I read it last, partially because I was full of a new found poststructuralist hatred of utilitarianism, and partially because even though I was a promoter of vegetarianism, it was all about the environment and nothing about animals themselves.
Reading it now, I am really taken with it. Sure, there are large parts I disagree with or would do differently (and his short history of specisism reveals how much better at genealogy people on this side of the philosophical divide are at that sort of thing), but it's smart, politically compelling, a strong mixture of nuance and moral outrage. If you haven't read it, or haven't read in a long, long time, I suggest picking it up. I'd be more than willing to discuss it with people. I am, in general though, surprised by how much people doing "critical" animal studies often wish to immediately distance themselves from Singer. It's fashionable, but I think it would be intellectually disingenous for me to do so at this point. I find Animal Liberation no more or less problematic than I find either Derrida's The Animal that Therefore I Am or Agamben's The Open.
Speaking of Derrida, I taught the first part of The Animal ... right before I started teaching Singer, and one of the weirdest things is that I am pretty sure that in many ways Derrida's The Animal that Therefore I Am is a response to Singer's Animal Liberation. A paper still remains to be written on this "secret" dialogue, but if there is interest I might post some of the things that make me feel this way.
EDIT: I know I said it was fashionable, but before I forget, I want to note two serious thinkers who obviously don't feel the need to automatically distance themselves from Singer. Leonard Lawlor and David Wood have both at least made footnotes supporting that there is a strange relationship between Derrida's thought and Singer's.