A note about countries - starting with the Mango update, the list of countries to which you can sell apps to (and from) is ~doubled, covering some extra ~2 billion people compared to the original list The freshly added countries are Brazil, Chile, Colombia, Czech Republic, Denmark, Finland , Greece, Hungary, India, Japan, Korea (South), Netherlands, Norway, Poland, Portugal, Russia, South Africa, Sweden, Taiwan

Still, if you're a developer outside these, not all is lost:

In China, Israel and Luxembourg, developers can begin submitting apps directly to the Marketplace, while other global programs allow developers from unsupported countries a way into the Windows Phone Marketplace. This includes Yalla Apps, serving 69 Middle Eastern and African countries, App Port, supporting 13 countries in East Asia, APPA Market with 19 Central European countries, and Device7 and MTell, both supporting China.