KellyMom: Possibly the best breastfeeding resource online. Find out what medications are safe to take while breastfeeding, how long your expressed breast milk will last in the fridge, how to increase supply, and the answer to almost any other question you could possibly have about your boobies!
Exclusively Pumping Board at iVillage: I am not an active member of this board, but it answered so many questions for me when I first began pumping. I remember scouring the internet trying to find out how much milk was a good, normal amount to be pumping - all the nurses in the hospital would say was "every mom is different!" Which is true, but I just wanted a ballpark estimate. I found it, and lots of other useful information, here. As always, when reading forums, consider the source. Not everything posted here is gospel truth, but there is a lot of good info.
My Posts About Pumping:
Ode to Reglan
Pumping Milestone: 5 months!
Pumping Milestone: 6 months!
Pumping Milestone: 9 months!
How Do You Measure A Year (Of Exclusively Pumping)?