I've used Cruise Compete for my past 2 cruises and had good results and prices with each trip. Most recently, my trip was bid on by 5 travel agents. Be patient - some agents took 5 days to submit a bid.
I eventually ended up going with Cruises-n-More, an American Express affiliated travel agent. After they bid on my cruise, I was provided a link to their web site and the actual booking and payment was done online - including cabin selection. The experience was similar to booking on Orbitz but the price was lower. I never needed to speak with an agent (which made my experience all the better).