I have never felt more like a rookie in my life since I've started taking care of a baby, and the things that seem like they should be so simple are often incredibly confusing. Being the kind of guy I am I figured there must be some sort of book that would explain all of those random but very immediate questions (insert tired "these things don't come with a manual??" joke here). I checked out a few and I've found what I think is the best - Michel Cohn's, The New Basics : A-to-Z Baby & Child Care for the Modern Parent. (And no, not just because it's for the "Modern Parent," though I do like the title.)
It's written by a kind of "pediatrician-to-the-stars" in NYC (Jennifer Connelly is quoted on the inside flap) and he covers most every question a new parent might have in a very matter-of-fact, non-judgmental way. We use it so much my wife and I have taken to referring to it as "the book." How often should we be bathing her? Check the book. Formula with iron or without iron? Check the book. What exactly is "colic" anyway? Check the book. The advise I got on sleeping alone is proving to be invaluable.
It definitely doesn't take the place of a question for your kid's own pediatrician (or a quick call to mom), but for a reference it's great.