This African visas and passport requirement information is written with U.S. citizens in mind but other nationalities can also benefit from the general information provided.
The requirement of having a U.S. passport valid for 6 months is applied across all the countries in Africa except Gambia. The cost of the different types of visa range between US$7-US$100 and this is assuming that you are making your Africa trip as a tourist.
Apart from the information here, I have also compiled a list of relevant sites to help you prepare your travel documents correctly such as the US embassy sites and the respective government websites.
Please understand that African visas approval for your trip is going to take awhile, so give yourself at least 1-2 months of lead time.
South Africa
South Africa visas are not needed if you do not intend to stay longer than 90 days or 3 months and as the average South Africa safari covers a week you probably won't need one.
Kenya
With Kenya visas, it's slightly tricky. Those African visas can only be obtained from the Kenya Embassies/High Commission so here is a list of the Kenya Embassies in the USA. You will also find up to date travel document requirements there. You can also obtain it upon arrival at the Jomo Kenyatta International Airport.
Tanzania
Going on safari in Tanzania to see the Serengeti migration? Find out more about the visa requirements here
Botswana
No visa is required for U.S. citizens for up to 3 months stay.
Namibia
No visa is required for U.S. citizens for up to 3 months stay but you might want to have access to the US Embassy when you are Namibia. It's a big place with a low population density and wide open spaces so you need to know where to turn if you run into some trouble.
Zambia
Zambia African visas application forms can be obtained online. This country is considered to be the best kept secret when it comes to safaris so get there before everybody else realises this and it becomes overrun with tourists like some parts of the Masai Mara. For renewal of passport in Zambia, you can go to the USA embassy in Zambia to obtain a form.
Zimbabwe
For Zimbabwe, there are 3 types of African visas namely the double entry visa, the tourist single entry visa and the multiple entry visa. All are valid for 6 months.
Gambia
There is a slight twist for those visiting Gambia as your passport needs to be valid 3 months beyond your intended period of stay. Here are more details about the entry requirements.
Alternatively, if you are making a last minute vacation to Gambia, you will still be allowed entry but will be required to submit your passport to the Department of Immigration in Banjul within 48 hours to be issued a proper visa.