Due out January 31, the DVD has a lot of those vague extras that rarely live up to your expectations - things like "Designing Dune," "Production Notes," and "Special Effects" - but the whole extended version thing (Alternate ending! A fight scene we haven't seen before!) can excuse a lot of filler, if in fact that's what those features turn out to be. There are, however, a few extras that sound more interesting, like a new documentary and some behind-the-scenes stuff from personal collections. A commentary or two (in addition to not being a single-disc flipper - what the hell?!) is what this movie is really crying out for, but I guess we shouldn't be too picky if we're finally getting to see the movie in a form closer to what David Lynch originally intended.
Edit: There are more details about the extras, as well as some information about which version of the film Lynch prefers here. Thanks, Elrond.