if you google 'pop art family photo' loads of companies come up. Friends have just done some for me, such a fantastic unique present. Think these firms work from digital electronic shots, so you could always ask the parents to email you a nice 'close up' shot.
How about several bottles of very good wine or port which can be laid down until the new baby is 18 or 21? If you get a variety that won't be ready to drink for the next 17 or 20 years, no-one will be tempted to open it before then, and it's a nice treat for an 18th or 21st birthday celebration. Someone did this for us when we got married- 2 bottles of port, one for drinking on our 10th anniversary and one on our 15th. Can't wait for 2008!
What about naming a star after the baby. You can go online to the international star registry and they will name a star after the baby. The register is kept in a vault in Switzeland. A copy is sent to you and it looks beautiful when framed.
I once bought a set of classic childrens books for a christening present which seemed very well received. You could always buy something like a set of the Narnia books.