I recently went to Durban to attend a wedding. While I personally don't consider Durban at the top of list of places to go on holiday in SA, I will say that Durban is great for the sun and the surf.
In terms of tourist attractions, Ushaka Marine World is a great place to take the family. You can spend the day having fun at the water park, catch the dolphin show or get in some knowledge and check out the aquarium. The aquarium is themed to resemble a sunken ship with certain rooms even displaying some of the decor and furniture upside down!
Those who are brave enough can even venture into the shark tank where you'll be able to swim with some of the scary predators of the deep blue sea!