Yebo [pronounced yeah-boe] means Yes in Zulu. It also has the meaning of "Hello" as a reply to Sawubona, which means "greetings" in Zulu. South Africans use this one all the time, I know I do, especially with my kids.
Usage : Under our constitution you don't have to be chicken about politically jokes. Yebo, Nandos.
In the early 90s the Vodacom mobile network used this word in a lot of their "yebo gogo" commercials. Some of them were incredibly entertaining.