If it were me, I'd go to Peru. What appeals to me is the variety of things to do there. It has mountains, rain forest, and deserts. It has the history of the Inca's (machu picchu), interesting sites, and cities. I'd get around by biking, take trains, and then you'd have a good month to really explore the country.
I would suggest South Africa (being careful maybe to avoid the World Cup in June I think? ) Anyway my family and I spent 3 weeks there in January 2002 and had a blast! We stayed in Johannesburg as a base and rented a car and drove to Sun City, then we went to a game lodge called Ingwe for a week of animal viewing - amazing. We flew down to Port Elizabeth, rented a van and drove for a week down the coast on The Garden Route to Cape Town where we went to the Cape of Good Hope park and stayed in a B&B, just amazing coastline and scenery, friendly people, good weather, etc. Don't worry so much about the crime situation, I know it's a huge problem but I've never had any trouble there, you just need to be aware.
That's my two cents.