The south coast has some nice little rivers and a short drive over a weekend sees you in the kei for some really top class estuaries.
Some good rivers include the izotcha river, the 2 rivers in southbroom the names of which escape me, the mpenjati and umtamvuna rivers. You can also pop into gremlins and chat to Brendan he will sort you out with anymore info you need.
Just bear in mind that winter is not great for the rivers but once it warms up you can pick up some nice little kingies, garrick kob etc