When we had a baby last year, my older son was 3 (we didn't know the baby's gender either!!).
He actually waited in the waiting room with my parents and he was the first one to come in and see his new baby brother. He stayed with my parents while I was in the hospital.
Once we were home, we had a gift that was from the baby for him (it was a big chalkoard in his room, so we couldn't give it to him in the hospital). We also made sure that when people came to visit, they acknowledged my older son first. And as much as you can't ask people to bring gifts for the older child, lots of people did. I never really understood that, but now that I have 2 children, I do.
Some people also suggested to give your daughter a baby doll and she can "care for" her baby as you are caring for the new baby. This worked well when my niece became a big sister.
Be sure to give your daughter some "mommy time" and "daddy time" after the baby arrives. Its hard not to get frustrated, but if she ats out, its more about wanting attention.
The best is yet to come! Congratulations!
B.