Franschhoek, which means "French Corner" in Afrikaans, is a charming historical town in the Winelands that was originally settled by French Huguenots. The annual Bastille Day Festival celebrating this French heritage is an extremely popular event with local Capetonians and international tourists alike! If you'd like to check out this event, it is essential you buy your tickets (& make restaurant reservations) in advance!
A must visit for steak lovers! They have a "blue steak" on the menu, which is ultra rare and ultra delicious!
http://www.capetownmagazine.com/whale-watching-hermanus
Cape Town's new Museum of Contemporary African Art is a must for art (and architecture) lovers! The building was originally a massive "mealie" (corn) storage silo, but was recently restored and converted into a stunning work of art itself!
Pilanesberg is a great national park and game reserve about a 4hr drive from Johannesburg. We've had great luck on safari here, seeing all Big 5! We definitely recommend doing guided night and early morning game drives, the experiences can be vastly different. If you have a rental car, it's also easy (and safe!) to do daytime self-drives in the park (just don't get out of your vehicle except in designated areas).