Pearls are always nice. A classic gift that a child can even inherit later.
A nice pendant with the new baby's birthstone in it . . .
All depends on how much you have to spend.
Hubby has bought items at Donald Haack and Brownlee. My BIL has bought beautiful stuff from Skatell's and I have been very impressed with their staff. I have not personally bought anything from there but am thinking about having them design a ring for a stone I have.
I just got on their website and they have a 14 KT yellow gold "add a pearl" necklace for $79. So there is a wide price range of beautiful items out there. You could get that necklace, add a few more pearls to it, then you can buy more pearls every b/day, holidays, etc. (assuming your wife would like that). Or a black pearl necklace for $315 . . . you can spend a little or you can spend a lot!!!
Skatell's Manufacturing Jewelers - necklaces