It has taken until I became a grandmother to get this right.
1. If the family is registered at Babies R Us (or anywhere at all), buy something on their list.
2. If they are not registered anywhere, do one or more of the following:
a. Give a gift card that can be used anywhere, e.g., Visa or AMEX
b. Write a note with an invitation to a lunch out and take her shopping to pick something special she still needs/wants.
c. Give a gift for the mom-to-be instead of the new baby, e.g., a charm bracelet with one or more charms related to a new baby (little blue or pink baby shoe maybe) or spa/bath items to make her feel special.
d. Make a set of coupons for special favors, e.g., baby sit while she takes a well-deserved nap, home delivery of a favorite take out food, a bouquet of flowers brought with a smile, time to listen (the key on this is to include your time to support her not just some token gift)