You would want to request high floor, North Tower, outside of the curve (or even numbered room; same thing as outside of the curve). If you don't request that last part, than you could be inside the curve, facing out to the lake (which is beautiful but not facing the parks/fireworks). I would call Disney reservations and add this request to the reservation now, as the room may already be assigned if you wait to put it in via online check in. I did this exact request in May, and they got it perfectly. We were in room 8410, a 1 bedroom, very close to the middle of the tower, could see the fireworks/space mountain/castle from our balcony. You may not want to do online check in at all if this view is very important to you, as if you wait and check in in person and the room is not a "good" one, you can ask them to see what else they have that you might like. As I understand it, once you do online check in, that is your room.
On page one of this thread, there is a link to a map of all of the rooms at BLT, views, etc. You can then know when they give you your room number if it is a view you want without having to go to the actual room. There is a great explanation of the room numbers in that thread. I will try to get the link for you...
http://www.disboards.com/showthread.php?t=2257082
