Yay for Up the Duff - my DH and I both like it - he doesn't like hearing all the gory details, and this book is light and fluffy and funny. My SIL gave me The Yummy Mummy's Survival Guide, another fun one that doesn't go into a great deal of medical detail, but is casually informative - like talking to a friend who's had kids.
What to Expect When You're Expecting is good for specific questions, I find, though I think the edition I have has since been superceded. Also Dr Miriam Stoppard's 'Conception, Pregnancy & Birth' was very informative too.