The Congressional Research Service (CRS) is one of the primary sources of information for policy makers in the US Congress. They have recently published three updated reports on the DPRK:
US Assistance to North Korea (PDF)
Mark Manyin and Mary Beth Nikitin
May 20, 2009
North Korea’s Nuclear Weapons (PDF)
Mary Beth Nikitin
May 5, 2009
North Korea’s Nuclear Weapons Development and Diplomacy (PDF)
Larry A Nikesch
May 4, 2009
You may download these papers to your computer or print them out, but they are worth being familiar with.
Other Congressional Service Reports on the DPRK can be found here.