MORE! MORE! MORE! Like detailed descriptions - with spoiler labels, of course. 
As you wish.
There are three documentaries, one by Houghton Mifflin, one for Fox TV, and one for Sci-Fi Channel. The third one is the longest, clocking in at around 38 mins, and it's also the most in-depth. There are a lot of clips and interviews used in mutliple documentaries and featurettes however, so you'll hear a lot of the same quotes over and over.
The Fox TV docu is nice too, mainly because of the behind-the-scenes clips, like:
LOTS OF SPOILERS AHEAD!
- Viggo cutting and eating a birthday cake and going fishing while still in costume.
- Orlando Bloom skydiving, snowboarding and bungie jumping.
The preview of the Special Extended Edition showed some interesting scenes that were cut like:
- Frodo and Sam seeing a group of Elves walking through the trees in the Shire.
- The cave troll in Moria hitting Boromir across the room.
- Galadriel giving Sam a rope and asking Gimli what he would ask of her.
- Bilbo writing his book.
- More scenes with Aragorn and Arwen in Rivendell.
And then there's the Two Towers preview, which is 10 mins. long. Here you see:
- Andy Serkis in motion capture sessions for Gollum.
- Peter Jackson introducing the new characters, like Theoden, Eowyn, Eomer, Faramir, and Wormtongue.
- An army of Uruk-hai attacking Helm's Deep.
- PJ talking about them finding the perfect location for Edoras, capital of Rohan.
- PJ talking about the huge miniature they built of the fortress of Helm's Deep.
There's lots more to see of course, but this is all I could remember off the top of my head.
