Apparently, as of 10:20 Pacific time, there are four states in which no presidential candidate won as much as 50% of the vote. According to this excellent Associated Press website, those 4 states are:
1. North Carolina: Obama 49.9%, McCain 49.5%, Barr .6%
2. Montana: McCain 48.6%, Obama 48.1%, Paul 2.1%, Nader .9%, Barr .3%
3. Indiana: Obama 49.9%, McCain 49.0%, Barr 1.1%
4. Missouri: McCain 49.6%, Obama 49.1%, Nader .6%, Barr .4%, Baldwin .3%.
As the night goes on, these percentages will change slightly.