In keeping with the "tourists in our own backyard" idea, we went on a bus tour of Cape Town during December.
The company offers two routes, the blue peninsula route—presumably more naturey—and the red city route, which we took.
The main point for setting out and completing the journey is the V&A Waterfront, but you can start anywhere on the route and buy a ticket on the bus. We opted to start at the Waterfront, hopped off and took a stroll around the Greemarket Square area, then continued on from there to Camps Bay where we had lunch. We finished at the Waterfront again.
And truth be told it is a totally worthwhile endeavour even if you don't hop on and off much. The commentary on the bus is quite good, and it's available in many languages—including Japanese! You can get a great overview of the city's history and recent happenings, as well as bookmark all the places you might want to visit on another occasion.
And if you get a good seat on the open top part of the bus you can take pretty good pictures. As you will no doubt note, I went a bit nuts with the historical buildings in crazy two tone colours. I can't help it, I adore them all.
UPDATE 2012: More recent Cape Town wanderings.