we just booked for 10/12/02 Western cruise and got an extraordinary deal (FL Res)
I'm not a strong believer that you receive better deals if you book early. However, the later you book, the less choice you have of cabins.
My advice is to find a knowledgable "cruise only" agent such as Cruise One. Also, although I've never used them myself,
Dreams Unlimited seems to be the agent of choice on this board. In addition, the time of year you cruise will determine the cost. We prefer to cruise in October, which although technically hurricane season, has never been a problem after 7 cruises. We find the weather to be more tolerant than the summer months, and the prices can't be beat. The one caveat is that your kids will be out of school for a week, but heck, they only live once! If you don't want to cruise in Oct, we also enjoyed mid December, on or about 12/15. You still get the value season pricing, and the added benefit of enjoying the ship all "decked" out with holiday decorations....we went last 12/15 on 7 day Eastern and had a great time.
I hope this helps...good luck.