The motion picture trilogy (theatrical editions, not the much longer director's cuts) will be coming out in a very nice looking box. No official release date has been set for this, though it seems online rumor has it that Peter Jackson will not have time to finish/bless this release until 2010 since so much work is going on with The Hobbit movie preparations.
Personally, I have a sneaking suspicion that there will be a second "extended edition" release on Blu-ray about 6 months to a year after the theatrical edition goes on sale, to get the core fanbase to buy the set twice (just based on previous studio behavior). Post your thoughts in the comments.
UPDATE: Bill Hunt over at The Digital Bits has some good inside information, and reports
Sources close to director Peter Jackson have informed me that he's saving the extended editions of the films for an "ultimate" box set release closer to the debut of the new Hobbit films - that's why these BDs are set to be theatrical only. That's obviously not going to satisify every fan, but it gives them something in the meantime. As was the case with the original DVD release, at least you're now aware in advance that a more elaborate release is coming eventually if you'd prefer to wait for it. For Warner's part, I've officially confirmed with the studio that this initial Blu-ray release is real and it's coming before the end of this year, but I'm told it won't be officially announced for another few months yet. So you should probably still consider this release to be semi-official and subject to change. Just FYI.