With Kim Jong Il dead, and his twenty-seven-year-old son his immediate successor, although probably with some sort of regent/advisor, nobody knows what is likely to happen in the short or longer run. South Korea has gone to alert status, because one way North Korea has historically dealt with uncertainties within has been to provoke someone else.
If you want to follow the speculation, here's some.
This is more a news article. The United States was just about to offer another round of food aid to North Korea, which is verging on famine conditions once again. That might have led to further talks on North Korea's nuclear program, but it appears that there will be a month of obligatory mourning in North Korea while those in power reassess their situation.
A broader look at the nuclear talks.
More links at Nuclear Diner.
North Korea at night, illustrating the oppressiveness of the regime and consequent lack of economic development, the same factors that lead to famine.
Lots of biographical pictures of Kim Jong Il.
From the BBC: a lineup of people and nations affected by Kim's death.
Steve Clemons lists people who are among the best placed to provide some insight. None seem to have published anything on Kim Jong Il's death yet.
Howard French: Crazy like a fox.
Christian Caryl: North Korea’s Not-So-Simple Succession.
Michael Hirsh: How Kim Jong-Il Became the Most Successful Dictator in Modern History.