South Africa
Lets start South.
Cape Town - colder water - drysuit diving IMO.
Lots of wrecks, Great Whites (open water or cage diving), a lot of shore entry dives.
I do not know the dive ops there at all - always just dive with friends.
Protea Banks - Kwazulu Natal South Coast (Shelly Beach)
Warmer water, deepish dives (30m - 35m), Bull Sharks, Tiger Sharks (sometimes).
About 11km offshore. Lots of current.
African Dive Adventures.
Aliwal Shoal and surrounds - KZN just South of Durban (Umkomaas).
I do not agree with Slipslop about Aliwal Shoal. Yes you can get currents here, but some of the best diving I have done was here.
Spotted Ragged Tooth Sharks in winter. Not much coral, but lots of life.
Dives from 10m - 30m
www.seafever.co.za (there are a few operators there but this is who I have been using for over 4 years).
Sodwana - KZN North Coast
Stunning diving from 12m - 30m.
Lots of great Coral areas, Whale Sharks in Summer etc.
Some of the most relaxing I have ever had.
Coral Divers or Sodwana Bay Lodge Dive charter.
Mozambique
There is lots of diving all along the Mozambique coast.
We have just returned from a two week holiday at Ponta Malongane in the South of Moz.
Warm water dives from 6m - 45m.
Malongane dive charter or Simply Scuba at Ponta Do Ouro.
Lots of diving further North in Mozambique (do a web search for Tofu Scuba).
Most of our diving is done of RIB's which launch through the surf - can be pretty exciting.
KZN and Mozambique best in Winter months.
PM me if I can be of further assistance.