Call airlines directly. Johannesburg is a major travel hub, so getting a flight with a well-known carrier will not be a problem. KLM, British Airways, Lufthansa, South African Airways and American Airlines are just a few. Most have 24-hour , toll-free numbers to call. If you like the price and the schedule and have your credit card handy, your ticket can be booked right then and there.
Browse the Internet. There are some very useful travel websites for booking flights. For example, www.lastminute.com is highly recommended for cheap, low budget travel.
Check out what your local travel agents have to offer. Even though they have taken quite a hit due to the expansion of Internet travel sites into their line of business, a good travel agent will be able to give you useful and insider advice on hotels, tours and sites to see.