If friends or relatives have recently added a new baby to the family, a thoughtful gift from you can make it easier for them to acclimate themselves to the new arrival.
Supplies for the baby are always good: cloth or paper diapers, baby shampoo and soaps, clothes and toys for newborns. But also think in terms of convenience and time-saving gifts. If the family has a freezer, consider cooking and freezing a week's worth of meals, so that the new mom can simply pop one of the meals into the oven in order to have a home-cooked supper. Buy a month's or year's membership to a diaper service. Or offer to show up a couple times a week to help with the housework, or to do the grocery shopping.
It's great to be practical, but don't forget to pamper the new mom, too. A bouquet of flowers or a gift basket filled with gourmet chocolates will be a more than welcome luxury. Beyond that, friends may want to combine forces to get the new mom out of the house; one can offer to baby-sit while others take mom out to lunch, a concert, or another favorite activity.
Don't forget Dad! He will appreciate the gift of a box of gourmet chocolate cigars to pass out to his friends in celebration of the new baby. (So will Mom, who will surely welcome a delicious alternative to smelly cigar smoke.)