theo there are lots of fish that would go well with those you have already, but you need to look online and do some research into the fish you like and whats avaialble in SA. If i were you id go to a good LFS, and see what fish that have that you like. then get the name of that fish and go home to research (this is WAY preferable over asking the lfs and you can plan your tank like u want it, not what they want to sell you!). then go back to get the fish that you want in a reccomended stocking order. I know its a pain planning a tank and resisting impulse buying but it realy makes life easier in your tank later.
you can have a look at a number of tangs though, scopas, convict, regal, sailfin, yellow, blond naso, naso are all good fish to add to that sized tank. Note im just pulling some names off the top of my head, there are lots more you could add to that list.
you could also look at an algae blennie (great vallue for money and awesum to watch even if he is a little ugly), midas blennie, gobies, dwarf angles, chromis etc. Lots of choices.....so go find the fish you like the look of and research that fish, then go back to get it.
i say go look at a lfs rather than hunting pics on google as the true life colours are ofetn different from photoshop and you can get a better idea of the shape, behavior and requirements of a fish when u see it yourself
, but having a look at id data bases online will also give you good ideas.