Throughout the course of the previews today, I did a little digging, and we have learned of the existence of two previously unknown locations in Fallout 3, and clarified the purpose of one of the previously known locations.

First, let's start with Paradise Falls. We all know about this town from the concept art that Bethesda released. What we did not know until today, however, was that Paradise Falls is a slaver community. From the Gamespot preview:

When you reach the outside world, you'll find yourself in the blasted wasteland in and around Washington D.C., a departure from the American West seen in the first two games. This is an area teeming with wild creatures and rival factions, such as the Brotherhood of Steel, which defends the remnants the capital; the Slavers who occupy Paradise Falls, a converted strip mall; and the super mutants, tough-as-nails humanoids looking to take over

Maybe we'll find Sulik's family there.

And now for the two previously unknown towns. First up is the town of Springvale. At this point, we don't know anything about it, other than the fact that this is a screenshot of it:

We know a little more about the new location Ten Penny Tower. This location can become accessible as a result of your actions in Megaton. As we have learned in various previews, Megaton's community is formed around an unexploded nuclear device. If you go to Moriarty's Saloon in Megaton, you'll find a man by the name of Mr. Burke who, as we learned from the IGN preview, "represents interests that would like to see Megaton wiped off the map and are willing to pay you to sabotage the bomb." If you do blow up the bomb, thereby completely destroying Megaton and all of the quests you didn't do in the town yet, a new location becomes accessible. Gavin Carter talks about it in his interview with Gametrailers.com:

You play [the Megaton quest] through the "bad" way and blow up the town, you erase everything in Megaton: all the quests that you might have gotten in there are now gone. But it opens up a new area, Ten Penny Tower, that you wouldn't have opened up if you didn't blow up the town. And that place has new quests, it has new items that you wouldn't have gotten.