Energy
Eskom
Eskom is a state-run power company.
Sasol
South African Coal Oil and Gas Corporation is an energy and chemical company based in Johannesburg; it is the world’s first – and largest – oil-from-coal refinery.
Finance
South Africa's Big 4
Standard Bank
Standard Bank Group, with its headquarters in Johannesburg, is one of South Africa's largest financial services groups with activities in 20 African countries and other key markets worldwide.
First National Bank (FNB)
First National Bank, a division of FirstRand Limited, one of the largest financial institutions in South Africa, operating in nine key African countries.
Absa Group
Absa Group Limited (formerly Barclays Africa Group Limited) is a South African financial services group.
Nedbank
One of South Africa's "big four" banks, originally founded in 1888 in Amsterdam, Netherlands, as 'Nederlandsche Bank voor Zuid-Afrika.'
Food & Retail

Canal Walk food court in Cape Town.
Image: Gilbert Sopakuwa
The Bidcorp Group is a Johannesburg-based broad-line food service company.
RCL Foods
The South African consumer goods and milling company was founded as Rainbow Chicken Ltd in 1960.
Shoprite Holdings
South African supermarket retailer with 2400 corporate stores and 513 franchise stores.
Takealot.com
The e-commerce company based in Cape Town is the country's largest online retailer.
Woolworths
One of South Africa's largest retail chains, not affiliated with the Australian supermarket chain Woolworths.
Media and Internet
Independent Online
IOL is a news and information company that provides online versions of several South African newspapers, including The Star, Pretoria News, The Daily Voice, Cape Times, Cape Argus and others.
Naspers
Naspers is a multinational holding company headquartered in Cape Town, active in publishing, online retailing and venture capital investment in internet technology with stakes in stake in Prosus and wholly owns Media24, Africa's largest publishing company.

The Sishen iron-ore mine in the Northern Cape Province of South Africa.
Image: ESRI, Maxar
Anglo American
Anglo American is a multinational mining company founded in Johannesburg in 1917; it is the world's largest platinum producer and is now headquartered in London, England. The company owns the De Beers Group, a diamond mining company founded by Cecil Rhodes, the founder of the British South Africa Company.
AngloGold Ashanti
AngloGold Ashanti Limited is a global gold mining company based in Johannesburg.
Gold Fields
Gold Fields is a global gold producer with nine operating mines in Australia, Peru, South Africa and West Africa (including the Asanko Gold Mine joint venture).
Impala Platinum
The South African mining group is based in Illovo, Gauteng. The company primarily mines platinum and palladium, but also rhodium and nickel.
Kumba Iron Ore
Iron ore mining company owned by Anglo American that operates the Sishen mine near Kathu in the Northern Cape province.
Telecommunication
MTN
MTN Group, headquartered in Johannesburg, is a multinational mobile telecommunications company operating in many African, European and Asian countries.
Vodacom
Vodacom Group Limited is a South African mobile communications company.
Cell C
Cell C Ltd is a South African mobile company headquartered in Randburg (Johannesburg).
More companies of South Africa.

Wikipedia's list of companies of South Africa.