babycenter.com
This is a great site for parents. You can register free and receive newsletters related to issues you are facing with your children. A wonderful tool for first time mothers.
Family doctor.org and KidsHealth are great sites if you have questions or concerns about medical issues. Of course, you need to contact your doctor if you have concerns regarding your child's health, but these sites are helpful references.
Check this site out for parenting tips on child development
Common Sense media offers "trustworthy information to help manage their kids' media lives."
A great culmination of articles, advice, and tools for step parenting.
As they get older, it sure gets harder. Check out this site for tips, advice, and other tools for parenting teenagers.
Autism speaks is a great online resource. Even if you don't have concerns with your own children, you can still support their mission.