The sets i want to see the most are:
1. Isengard
I know this would be a very hard location for lego to build but i believe they could do it and I'm not just talking about othanc but the pits of Isengard along with all the machinery and towers we see in the film. it would be a very large set indeed and i can't see how lego could build this without using at least 2500 pieces. this is my favourite location in the films.
Figures included: Saruman the white, Grima Wormtongue, 2 Dunlendings, 4 uruk-ha.
2. The bridge of Khazad-Dum
Seeing as lego have already made a mines of Moria set which includes Balins tome, I believe we need the other part of Moria and in my opinion where the greatest scene in the fellowship takes place. the set would be of medium size with the main bridge itself, two small parts of land on either side of the bridge.
Figures included: A fully brick built Balrog of Morgoth, Gandalf the Grey, 2 goblin archers.
3. Barad-dur
Saurons great tower would be a very large set with many pieces. I would like to see the set come with the tower itself with a long bridge at the bottom so orcs can march across. Of course the eye of Sauron would be at the top hopefully with turnable bricks so we can adjust which direction the eye is watching.
Figures included: 6 Mordor orcs.
4. Rivendell
Another large set which would include the main building which we see in the films where the elvish library is and the room where the sword Narsil rests. Hopefully the council of Elrond will be part of this set also. The main bridge in Rivendell should also be featured in this set.
Figures included: 4 Elvish warriors, Arwen, Elrond.
5. Hobbiton
Large set with 4 different hobit houses each one being very different and unique and amongst those houses bag end.
Figures included: Rosie, Frodo, Bilbo, Sam, Merry, Pippin, 2 random hobbits.
I hope you've enjoyed reading my ideas.