I'll second this. The DVD extended version has many small details that had to be left out of the theatrical release for brevity. It adds about 30 minutes to the whole thing sprinkled in and out of every major scene, making the movie just a bit more true to the book.
It also contains two more DVDs that detail the making of the film, which is interesting in its own right. Also Peter Jackson explains why certian scenes were cut from the theatrical release. He says the the first movie was to be Frodo's story, and therefore some scenes which would flesh out some of the other characters were chosen to be removed.
IMHO this is the best DVD set ever made. The amount of "making of" information included is staggering. I love that sort of thing and enjoyed the second two disks almost as much as the first. Remarkable how much planning went into making those movies.