photo credit: Aah-Yeah
Carnival Cruise Line offers some great rates if you book in advance with their Early Saver Rates. Carnival states that you can save up to 20%. To qualify for the special rates you must pay a non-transferable and non-refundable deposit. Bookings must be made 3 months in advance for 5 day or shorter cruises, and 5 months in advance for 6 day or longer cruises to get the special rates.
One bonus I have seen is that you get to pick your cabin instead of booking a guaranteed cabin, and the price is usually the lowest available. Price protection is also a feature of the Early Saver Rate.
Please visit their webpage for full details on the Early Saver Rate terms and conditions.