To allow passengers to adjust to new security restrictions, many carriers relaxed their luggage restrictions. Today, it was reported that Northwest Airlines resumed its charge of $80 for passengers who wish to check a third bag.
American and United have resumed charging as well. For restrictions on your carriers, please consult their website. The average for most U.S. carriers is two bags, each to weigh no more than 50lbs. Some carriers still use the older allotment of 70lbs, but with rising fuel costs, carriers have been forced to give less for free. For excess weight or pieces, expect to pay a charge as airlines are enforcing these allotments more strictly as a source of revenue.