We did the dolphin cruise last week. We booked right at the Disney activities window by the pool. We had just us 4 and the guide in a small boat. We had a GREAT trip. We saw many dolphins and even a 2 week old baby dolphin! Very close, may 4 feet from boat.
I have also heard of Low Country Tours and Cpt. Scott. I don't know if this is the same company or not?? We met our guide right at that office, he walked us out of the resort and to the boat at Shelter Cove. He even pulled his crab trap and showed us about 15 crabs.
If you can, do the activities on Tues. night (The Star Spangled BBQ). It was TONS of fun and we watched fireworks with everyoned else right around the campfire, toward the dock into the marsh at Disney. The fireworks barge is right there.