WellStart: The user manual and digital recordbook for your child Dr Heidi Worthington, Dr Soraya Bate and Dr Philip Worthington

First off, it's not a paper book - but it doesn't fit anywhere else in these reviews. It's a computer program that acts like an interactive book and baby journal where you can store all your videos and photos to record your child's life.
I bought it at the Baby Show a couple of weeks ago, and it was a bit of an impulse buy because I hadn't heard of it before. But now I've got it I think it's great - there's loads of information about your baby's development (apparently it also covers pregnancy but I got it too late for that - maybe next time!).
It works as a calendar. You put in your baby's birthdate, and it gives you information on when to expect to see different behaviours developing, but without making you feel that your baby "should" be doing something by now, or that they're falling behind. Every time I start my computer up I get a short list of things to look out for, that i can click on to learn more, or to record that they've started doing that.
For me, the best part is that it reminds you to record lots of little details about your baby growing up that you might not otherwise think to record. I'd really recommend it to other mums, and already have done to two friends with new babies.