La Leche League: mother-to-mother support in person, on the phone and via email. LLLI.org is an excellent source of articles about the science and art of breastfeeding. Canada United States United Kingdom Anywhere
Kellymom.com: my favourite resource for quick, evidence-based advice that’s easy to understand, but referenced so that you can look up the primary source yourself
NBCI: in addition to Dr. Newman’s various protocols, these are some of the best video resources on the web. If you need to know whether your baby is actually swallowing milk, this is the video series to watch
Books (these are my Amazon links, but buy them elsewhere with no hard feelings)
The Womanly Art of Breastfeeding: the 2010 edition is vastly improved over the older, folksy-editions (which still contain good, helpful information)
The Nursing Mother’s Herbal: an excellent resource for information on using herbal remedies during lactation, something that’s vastly lacking in most sources. Also, just a generally good breastfeeding book
Motherisk at the Hospital for Sick Children (Canada): a free hotline and web resource for drug risk information during pregnancy and breastfeeding.
Infant Risk Centre at Texas Tech School of Medecine, Amarillo (United States): a free hotline and web resource for drug risk information during pregnancy and breastfeeding.