I will recommend Singledivers.com as well. I have made numerous trips with them, and have not had anything but wonderful experiences. There are numerous trip options every year, and the questionnaire you fill out before the trip goes a long way in matching you with a compatible room mate and dive buddy. It sure beats the experiences that I have had with roommates that I have been matched with on liveaboards in the past, or having to pay a single room rate.