You can try hotels.com or priceline. You can get a lot of hotel deals online. Once you get a price you might want to compare it to the Hotel website, though. Many hotels say the lowest prices are on their own sites now.
Lots of the hotels have "park and cruise" specials so that you can leave your car at the hotel, be shuttled to the pier (often for free) and shuttled back to the hotel when you return.
Carnival Elation March 11
Carnival Imagination Sept 07
Carniival Sensation Dec 06
RCI Sovereign of the Seas Sept 06
Carnival Miracle Sept 05
Carnival Glory Sept 04
Carnival Fantasy Jan 04