Awarding Organisations, previously known as Exam Boards.
Below I have listed the main awarding organistaions, with links to their websites. These websites are a very useful source of information, giving details of all their available qualifications, syllabus information, exam timetables etc. Much of the information on the sites is probably available to you in school, but the websites are worth a visit because there is so much information available in one place.
University of Cambridge International Examinations (CIE)
Independent Schools Examination Board (ISEB)