Apple has added some more talk radio stations to iTunes Radio. In addition to the recently added NPR News and Culture station, they have added ESPN News and Sports.
There are also five other NPR stations that show up when you do a search when creating a new station:
It seems likely that more NPR stations will show up in the search in the near future. I would also expect that iTunes Radio may add a Talk genre to make it easier for users to find these stations, as the service evolves beyond simply a tool to try and get users to buy music from the iTunes Store.