Hi B.,
Congrats and your new little one!
I can not say enough good things about Bravado Nursing Bras. I have 3 of their "Original Nursing Bras". They are well-designed and super comfortable. The biggest plus is that each bras fits a range of sizes, so as your breasts grow and shrink, over time and even throughout the day, your bra will still be comfortable.
I was a 36DD before I was pregnant, and I know how hard it is to find good bras, much less good nursing bras. The ones at Target were so cheaply made, I took one look at them and walked away in disgust.
Brand new, Bravados are in the $40 range. I actually bought all of mine off of Craigslist and eBay. You know, some women only nurse for a short period, so it's easy to find used Bravados.
http://www.bravadodesigns.com/page.asp?ID=613
One sizing tip: If you look at their sizing chart and find you are in between two sizes, consider going with the smaller one. They are super stretchy, and you will end up swimming in your bra if you go with the larger size.
You asked about breast size. You know what--there's really no way to predict or judge what's going to happen when. Once I was pregnant, I want up to an "E" cup. I wore Bravados during the last part of my pregnancy and while I was nursing. Since the bras fit while I fluctuated, I wasn't really aware of what cup size I was.