I wasn't that impressed with What to Expect the Toddler Years, but there was a handful of good information. I'd say get a used copy, then get "Happiest Toddler on the Block" (I hear there's a video or something that goes with it as well...maybe some other mama can confirm or deny that).
Your main concern won't be what to expect, but how to react when it happens...when you realize that your precious bundle has slowly usurped your authority and taken control of your household. I don't really know how to say when you know that's happened, but you'll call a girlfriend in tears because you "can't take it anymore" and "will never have another child" (of course, you will find out you're pregnant soon after this conversation), and you need to go to Starbucks right away.
I had to edit my response to agree with the mom about getting "Parenting with Love and Logic" after she's 2.