Refer to the country by the correct name… the Democratic People’s Republic of Korea. I can tell you from first-hand experience that they don’t like being called North Korea. Democratic People’s Republic of Korea, DPRK, or Korea were the three choices that were given to me when I visited Pyongyang in 2009.

Here are some other indicators:

• http://www.korea-dpr.com/, says it is the official web page of the Democratic People’s Republic of Korea
• http://www.kcna.co.jp/index-e.htm, which is a major news outlet for the state, says News From KOREAN CENTRAL NEWS AGENCY of DPRK (Democratic People’s Republic of Korea)
• http://usa.chinadaily.com.cn/, which is one of China’s major publications, calls it DPRK

Heck, in an article on the China Daily site, they even go so far as to correct the president:

“North Korea (DPRK) will achieve nothing by threats or provocations,” Obama said during a press conference in Seoul after talks with his South Korean counterpart Lee Myung-bak.

http://usa.chinadaily.com.cn/world/2012-03/25/content_14908165.htm

Look, we’re talking about a country that has the fifth largest active army, the capacity to launch rockets/long-range missiles, and might be developing nuclear weapons.

If the US is really intent on reaching-out to the people and/or government of the country, they can start by using their chosen name.