The College Board: https://www.collegeboard.org/
The College Board administers the SAT, a standarized test typically required for admission to many US colleges and universities. They also adminster the SAT II Subject Tests. Test dates and registration deadlines can be found here. College Board also provides a useful college search tool which can help you create a list of schools for which to apply.
EducationUSA is a network of advising centers across the world, which provides accurate, comprehensive, and current information about pursuing higher education in the United States. Nearly all African countries have an EducationUSA advising center where students can get resources and advice for free. Find the EducationUSA center in your country here.
Competitive applicants with limited means may also be eligible to receive funding for some up-front costs to a US application such as testing, application fees or airfare through the EducationUSA Opportunity Fund. Learn more about that fund and similar initiatives through EducationUSA here.
African Leadership Academy: http://www.africanleadershipacademy.org/
The African Leadership Academy is a high school in South Africa committed to developing the continent’s future leaders. Most students attend ALA for the two year pre-university course, based on the Cambridge A Levels and ALA’s unique curricula in Entrepreneurial Leadership, African Studies and Writing and Rhetoric. They also host a Gap Year program for students in between high school and university, as well as summer program, amongst others. Many ALA graduates go on to attend university in the United States.