Thanks to a question at AskMetaFilter, I learned something I should have known years ago: the ISO country code for South Africa is .za because it’s from the Dutch Zuid-Afrika. The Wikipedia entry explains:
This is a legacy of when Dutch was an official language in South Africa, before being replaced by Afrikaans, in which the name of the country is Suid-Afrika. Afrikaans joined English and Dutch as an official language of the South Africa in 1925, and in the South African Constitution of 1961 Dutch was removed as an official language altogether, decades before .za was introduced. However, the .sa domain is used by Saudi Arabia and ZAR is also the ISO 4217 currency code for the South African Rand.
I had vaguely assumed it was based on some name comparable to Zaire and Zambia.