If you're coming from a major international country, such as Europe, Canada/UK, Oz/Nz, then you are entitled to a 90 day free visa. You just rock up and you're all good to go. Very easy. The only noticeable countries that aren't entitled to a 90 day visa are Poland, South Korea, Thailand, Turkey and a few South American countries.
However, it's not all bad news as most other countries are entitled to a 30 day free visa.
To enter into South Africa you'll need the following:
If you want more information you can call the Home Affairs Contact Centre on +27 11 461 9252
If you need to apply for a visa you can do so here:
Dependent on length of stay requested. Permits may be extended if done so 30 days prior to expiry of original permit.