I've got a few favorite links, and I bet others have some to share as well.
The Well-Rounded Mama: http://wellroundedmama.blogspot.com/ This blog emphasizes size acceptance for fat pregnant women, especially when it comes to maternity care.
She also runs Plus-Size Pregnancy, which is less updated but has a wealth of info: http://www.plus-size-pregnancy.org/
The Adipositivity Project: http://adipositivity.my-expressions.com Contains nudity - NOT SAFE FOR WORK! This is not specifically related to motherhood, but sometimes we need a reminder that beauty goes beyond what we see on tv/in magazines/in advertisements. This site's aim is "to widen definitions of physical beauty. Literally." through photography of fat bodies.