This is helpful year-round, but especially so during the holiday season. Instead of having to request notifications from the place you purchased items from, or manually entering the tracking number, they just automatically notify you about any packages coming to your house.
USPS: Informed Delivery
UPS: Μy Choice
FedEx: Delivery Manager
Parcel sorting facility in China
snuzet: Also if going away easy to have mail held via Usps website.