[mschwarz]

First off - congratulations on the baby!

I think you can't go wrong with either choice. However, I think the flash might be the way to go for now - only because I imagine you will be taking a ton of indoor pictures of the baby. While the lens can definitely help improve indoor shots (I have the 50mm f/1.4), I think the flash will give you more flexibility to catch shots you might not otherwise be able to get.

I've got the SB-600, and I've used it only as a bounce flash so far, but it's helped tremendously on just my D60 kit lens (18-55mm).

Either way - good luck, and post pictures of the baby!