Pongola -- this is a fantastic area just south of the Swaziland border. I would recommend staying at 'Shayamoya'. It is a perfect way to experience the African bush, with chalets that are just the right combination of luxury and 'roughing it' -- including outside (but very private) showers.
The Wild Coast -- West of Durban, this is the place to go for paradise-style beaches and a great hotel at the Wild Coast Casino.
The Drakensberg ('Dragon Mountains') -- one of the most beautiful parts of a beautiful country, many places to stay for all budgets.
The Midlands Meander -- this is a route through the stunning Natal midlands, with places to stop for food, shopping for local arts and crafts and lots of scenery. I would particularly recommend the Dargle Valley and Dargle Lavender Farm, a tranquil place to visit (and the smell of lavender is heavenly!). Budget well for purchases, some of which may be expensive but got-to-have-it items. The people you will meet make it worthwhile even if you buy nothing.