I have had good experiences with a firm called www.go2africa.com.

They deal on a land basis (so you can use your reward tickets for flights to South Africa) or can add in flights as well if you wish. They deal by emails with you, have a quick response time and I found there they took time to ascertain what you wanted to achieve from your holiday and recommend a lodge appropriate to your budget.

You get met at the airport and they can arrange for transfers to all hotels, side excursions, transfers to local flights, etc, etc. I found that the most difficult thing to organise via the internet is for flights to the safari lodges around the Kruger area which is where using a local agent was incredible helpful.

The main attraction of this agency was the ability to do everything through the internet (other than for payment).