The amount and type of animals you are likely to see will greatly depend on the region you visit.  Etosha National Park is home to 4 of the Big 5, which include the Lion, Leopard, Rhino and Elephant.  Buffalo is the only one of the Big 5 that is not present in the Etosha National Park.  Etosha is home to 144 Mammal species, including Zebra, Springbok, Oryx, Kudu, Eland, Impalas, White and Black Rhino, Giraffes, Damara Dik Dik, Steenbok, Brown Hyenas, Cheetah, Leopard and Jackals to name just a few.  Birdlife in Etosha is also very prolific, with a wide variety of endemic and migratory birds.
In the rest of Namibia, you are likely to spot some Oryx, Ostriches, Kudus, baboons, and warthogs.    And in the Caprivi and Okavango Regions, you can see crocodiles, hippos, roan and sable antelope and buffalo.
Along the coast of Namibia, you may see heavy-side dolphins, the cape fur seals, and rich marine birdlife.