When I was pregnant with my first son I bought what seems almost every book published about parenting.  After having my second son, there were a handful of books that I consulted and reread.  I donated all the other books, and have only kept a few good ones on my bookshelf.  Here are the titles that I found worth reading (twice):

1.  The Girlfriends' Guide to Pregnancy by Vicki Iovine.  I found this to be one of the more straightforward pregnancy books.  She is very candid and funny about what to expect during your pregnancy and childbirth.  She tells it to you straight, like your girlfriends do.  And if you like this book, she's got more for the months/years to come.  There's The Girlfriends' Guide to Surviving the First Year of Motherhood, The Girlfriends' Guide to Parties and Playdates, The Girlfriends' Guide to Toddlers, The Girlfriends' Guide to Getting your Groove Back, and Girlfriends' Guide to Baby Gear.

2.  Healthy Sleep Habits, Happy Child by Marc Weissbluth.  I think I read about 5 different books on trying to get my newborn to nap and sleep longer at night. This book was the one that helped me solve my sleep issues.  Weissbluth talks about the importance of a well rested child, sleep cycles, different temperaments, and how to help your child develop healthy sleep habits.   I've also used it to help my toddler transition from 2 naps to 1.  The author also helps with many sleep problems (nightmares, bedwetting, etc).  This is a must read for that sleepy-eyed parent.  I love this book so much I give it as a baby shower gift to new moms.

3.  The Nursing Mother's Companion by Kathleen Huggins.  This is a great resource for mothers that are breastfeeding.  It tells you what to expect while breastfeeding at the different stages of your baby's life and also addresses issues/concerns that may come up along the way. 

4.  Baby Bargains by Denise Fields and Alan Fields.  This book is a great resource to consult when you are buying (or registering for) baby gear.  It is a cross between consumer reports and parent-tested testimonials.  They give advise on how to shop for gear and key things to look for when purchasing, as well as good (and bad) deals.    They tell you what safety things are necessary, and gear that is a waste of money.  Major brands and manufacturers are rated and also written up with the pros and cons.  Make sure you purchase the latest edition of this book, to get the scoop on the newest gear.  They also have Toddler Bargains and Wedding Bargains.

5.  What to Expect When You're Expecting by Heidi Murkoff, Arlene Eisenberg, and Sandee Hathaway.  I only put this because it seems like everyone has it.  It is a good resource and talks about everything that is happening (or could happen) to you and your baby.  It chronicles a pregnancy month-by-month and answers pretty much any question you may have about yourself and your baby.  After this one, you graduate to What to Expect the First Years.