There's interesting news for Fallout 3 fans today which comes in from an interview with Bethesda's Lead Producer Jeff Gardiner over at Eurogamer. Gardiner reveals that the upcoming "Broken Steel" downloadable content pack for Fallout 3 will remove the current "ending" of the game and allow gamers to level their characters past level 20 all the way to a new cap of level 30.
"Along with removing the game's 'ending' with Broken Steel, we figure raising the level cap would allow them to [enjoy the game for longer]. We plan on raising it to level 30 - but it will be a long, hard climb to get there!"
There are three planned DLC packs for the game, with Broken Steel being the third, set for release in March of this year.

Update: After sending an e-mail to Bethesda regarding the new level cap on the PS3 version, we received the following statement:
"No, [the level cap] is part of the DLC and therefore if you don't get the DLC, you don't get the increased level cap."
It seems that since the content is exclusive to Xbox 360 and Windows, PS3 owners will peak at level 20.