Mollie, congrats on the impending joy!
I'll just add this: since you'll be around for a while after the birth, keep your camera out and watch for the wonderful interactions that will happen.
You can set up for some shots for sure, but since you'll be there when the baby is sleeping, being fed, cuddled, bathed, dressed and loved, just have the camera ready to go. That 50D coupled with the nice lens that you have will allow you to shoot in almost any setting and light conditions.
Keep the ISO high in low light and in all conditions keep the aperture open pretty wide. I often shoot newborns at 1.8 or 2.0. Just be careful where you're focus falls.
Shoot close up, but also back off every so often for the bigger picture when the parents are scurrying around. You can really tell a story about the first days of the baby's life.
I'd start by taking some pics at the hospital. Depending on where you'll be and what the mom & dad want photographed (maybe talk to them a bit before, so they won't be surprised), you could get a few really meaningful images. Just work with the available light.
I love to include hands in the photos, whether set up or spontaneous. There are few things lovelier than a baby being cradled by its parents.
Have fun, relax and look for things to happen. I hope you'll share with us!
Here are a few ideas from some of my pics:
The third one was taken on a bean bag covered with a soft off white blanket. Bean bags do work very well! Oh, and I don't use flash with them. Little eyes are pretty sensitive.