Take the time to tour the Makgadikgadi Pans National Park. I found it to be a savage paradise off the beaten track, with basic camps accessible by four-wheel drive and no lodges. If you go during the rainy season (although Botswana's rainy season means lots of roads are cut off!), you'll witness the second biggest zebra migration in Africa, with only the Serengeti in Tanzania pipping the post. Apparently you can witness up to 20,000 of these stripey beasts crossing its muddy basins!
I would have loved to have seen this, but, as with most tourists, I wasn't there during the rainy season. The middle of the dry season is, in my opinion, a good time, as the plains aren't too arid, which makes it easier to spot animals. The southern part of the park, which is close to River Boteti, is greener and home to wild animals all year long. Makgadikgadi Pans' other big attraction is Kubu Island.