Internationally standard paper sizes.

This Wikipedia article gives a comprehensive breakdown on the International Standard for paper sizes.

America uses their own paper sizing system with standards including Letter and Legal.

Other common document formats include:
Flyers: DL
Postcards:
Business cards: Standard – 90 x 55mm, low profile – 90 x 45mm
CD covers: jewel case: inserts – 120 x 120mm, rear tray
CD simg