We stayed at a really pretty hotel in Lobito that was steps from the ocean. The beach at the hotel was nearly deserted. We spend a lovely morning on the beach playing in the waves and resting under a big umbrella. The pool at the hotel was equally enticing and we spend a few hours there as well.
As for exploring, we managed to see quite a bit while we were there. In Lobito, we saw the port, the railroad, the beach, and a couple really pretty churches. In Benguela, we saw a bunch of the agricultural areas where the Portuguese use to grow sugar cane (now the Angolans grow corn, bananas, mangoes, etc), the Cuca (Angolan beer) factory, some of the military schools, and a couple of beaches. In Catumbela, we saw the beautiful Catumbela River (which we were told are full of jacares [alligators], some ruins of an old Portuguese fort and church, the nice new bridge, a local neighborhood and the big soccer stadium that was built for the African Cup in 2010.
We also went to the Chimalavera National Reserve but didn't get to see anything except the lodge and a random springbok that was hanging out there. There is no road through the reserve - you just drive along the main road. We stopped and had a packed lunch and tried not to melt in the heat of the day.