Bethesda Game Studios have published a series of five in-game videos of the forthcoming Fallout 3 on YouTube, the technology looks really impressive:

"Fallout 3 - Escape (1 of 5)" - http://www.youtube.com/watch?v=HUI0Up4AiQw&feature=related

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Updated 2021 : note that the above post is out-of-date, given this post was originally published in 2008, but is left here for archival purposes. As the original video on YouTube was removed, I have unlinked it above, however your can find the original E3 trailer for Fallout 3 here. I cannot tell you how many hundreds of hours I put into this game!