The Womanly Art of Breastfeeding
by La Leche League® International

This is an exhaustive source on breastfeeding, great to read in advance and keep handy during those first few months of nursing. Leans towards attachment parenting, so if that is a turn-off, choose another book and just go to the LLL meetings.

So That's What They're For!
by Janet Tamaro

A fun read cover to cover that will give you the same information as any other breastfeeding book, with a little humor added in.

Ina May's Guide to Breastfeeding
by Ina May Gaskin

This guide to breastfeeding is written in the same friendly and approachable manner as Ina May's Guide to Childbirth, while still teaching and de-mystifying the breastfeeding process.