We just got back from cruising on the Jubilee last Monday -- we had a ball! This cruise was planned directly through Carnival -- and I checked around it was the best deal that I found. We are looking at planning another cruise (of course no time soon) how is the best way to look for the best deal if you are looking way in advance?
The best prices are usually found on the internet web sites just before sailing. But, the best price is not always the best deal. A local TA who specializes in cruises who you can sit across the desk from may be the better deal for you.
Most cruises are discounted heavily near the sailing date to sell off the remaining cabins. In order to take advantage of these deals you must be flexible with dates and usually near the port so you don't have to fly to the ship. We all know waiting until the last minute to fly is expensive. More popular cruises will sell out in advance and last minute deals are not to be found.
Since you don't have a specific sailing date yet, its really hard to shop around for prices, i think you should call a travel agent - one who sells lots of cruises, ask them if they are running any group cruises in the future (best bets for pricing). The cruise lines don't usually release their fares more than 1 year in advance. You can get a rough idea from the travel agent.