Aside from the basic childhood immunizations you normally get, Hepatitis A, Meningococcal meningitis, Rabies and Typhoid vaccinations are highly recommended. If you're going to a Yellow fever prone area (I don't know if there are any in Africa, you'll have to do your research), it's good to get that taken care of as well.
You'll also have to look into malaria prevention. There are many preventative pills out there that you can take. There are also new pills you can take when you THINK you have it (though these, I hear, are not highly recommended, and they're pricey). I took Doxycyclene (a once-a-day pill to help prevent malaria) when I went to south asia, and the only problem I had was heartburn.
There are travel clinics in many cities across North America that I highly recommend you visit. They will be able to recommend vaccines and medication to you based specifically on where you're going. They'll also set up post-trip appointments to make sure you're healthy when you get back.