The section below Augrabies Falls is similar, and there is a one-day rafting trip above Augrabies which features some exciting but not radical rapids. The Gorge section of the Orange is a lot more technical and has some high-volume rapids.
The Vaal, a tributary of the Orange, has some fun little rapids and is very close to Johannesburg, so it's a popular destination for corporate trips. Also near Johannesburg, the Crocodile River offers a pleasant day out with some small and mildly challenging rapids.

The Doring River in the Western Cape has a short season towards the end of winter, and offers fantastic, quite technical white water, but it's pretty cold.

The Palmiet River is absolutely wonderful. It runs through the Kogelberg Nature Reserve and offers fantastic technical rapids and wonderful scenery. The trip offered takes one day and includes all meals and sometimes a visit to a winery.
The Molenaars is a very technical, white water river that only works for a few days immediately after heavy rain in its catchment area, so it's not easy to plan a trip. The Sonderend River is a smallish river where you can do a fun day trip or overnighter.

There are two trips on the Breede River: a one day wine tasting trip near Worcester, which is really just an excuse to have a lovely picnic and sample some local wines, with a little bit of paddling thrown in. Lower down, near Swellendam, two-day trips are run on some small rapids and quite rocky sections. This section is used mainly for corporate trips.

There is some fun canoeing in the lakes area of the Garden Route, especially Wilderness and Knysna Lagoon. Other enjoyable flat-water trips include the two self-guided excursions near Port Alfred, one of which is up and down the conveniently tidal Kowie River. The other is a short paddle up the Kleinemond River to a wonderful overnight spot, called Kayak Camp.