I can't believe nobody has mentioned New Zealand yet. It is one of the most beautiful, varied, fascinating countries on the planet. No visa hassles, English speaking, and some of the friendliest natives anywhere. Weather in Auckland and most of the North Island will be quite nice in March, temps in the 70s most likely. Lots of history and sights in and around Auckland. Make sure to head to Rotorua as well and see the hot springs, geysers and such plus all the native Maori displays and demonstrations. Christchurch is the most European city in the Southern Hemisphere, with a great tram ride up the mountain. And Queenstown is striking with its natural beauty and extreme sports. Don't forget Dunedin down toward Invercargill with its maritime influence and Scottish feel. NZ is absolutely incredible; you definitely won't be disappointed. The currency won't make things dirt cheap (but there aren't very many places where that's the case for US Dollar holders right now). But the NZD/USD rate is about where it was 12 months ago and sits at about NZD1.40/$.

If you really want Affordability along with Different and Intellectually Interesting, go for China. I'd start out in Hong Kong and see the sights. Go ahead and do the tourist thing there - Man Mo temple, Victoria Peak, Tsim Tsa Shui, etc. Take a half-day tour bus and just try not to roll your eyes when they take you to the "jewelry factory" to spend money. The exchange rate is still fixed at HK7.8/$ so Hong Kong is only as expensive as it ever is. While you're there, take the ferry to Lantau Island and see the giant Buddha. Then take a day and see Macau - really fascinating place with the Portugese influence. The Macanese currency is fixed at a rate very close to HK's and the currencies are easily exchangable. Stroll over to Largo do Senado and take in the architecture. Go see the old fort and ride up the sky tower, then down to the Lotus Flower temple. Have a bite and some pints at one of the pubs along the water before heading back to HK on the jet ferry. Then take the train or the ferry up to Guangzhou. The Chinese currency is fixed at R8.28/$, and you'll find prices much more reasonable than in HK. See the Sun Yat Sen memorial and the city museum. Take a tour of the city as well. Then fly up to Beijing (CAN-PEK) and see everything. You could spend a week in PEK alone. Make sure to get out to the Great Wall too. Then end up your visit in Shanghai (PVG) and soak in all the energy of the most dynamic city in Asia. You'll need a visa to visit mainland China, but not for Hong Kong or Macau.

I also agree with the others on Brazil, but safety must be a concern there if you're to spend any time in Rio or Sao Paulo. It's definitely affordable and the weather should be decent, but some caution should be observed in your planning.

Let us know what you decide! Good luck!