Most airlines have a 2 piece limit for international economy passengers, with neither bag exceeding 50 lbs. (23 kgs.), nor can either exceed 62 in. (158 cm.) or 107 in. (273 cm.) combined. For business and first class passengers, most airlines require that your 2 pieces of luggage do not exceed 70 lbs. (32 kgs.), nor can either exceed 62 in. (158 cm.) or 124 in. (316 cm.) combined. For an extensive list of the baggage allowances for international flights on specific airlines, please refer to this document.
Please note that the baggage allowances for domestic and US flights vary among airlines, and the individual airlines' websites will have the most up to date information regarding their baggage allowances.