Come visit Port Douglas. I think this is the best place to go diving on the Great Barrier Reef.
We stayed in the Hibiscus Hotel, which is a four-star hotel designed like a Balinese-style bungalow.
We went with one of the local boat operators (there are many to choose from) and arranged a day out on the reef. The boat left at 9pm and headed out to the reef. We had great weather and the visibility was amazing, with so many fish to see.
The boat supplied a buffet-style lunch and we rented the diving equipment on board. The cost is around $120 for the day, but it was definitely worth it -- a once-in-a-lifetime trip sometimes. I had friends from overseas with me and we had an amazing day.
To get to Port Douglas, you can take a 40-minute bus ride from Cairns or hire a car for a day or two. You will find some great places to eat out, either on the cheap or a more expensive seafood banquet.
The area is very laid-back with nothing to do but relax and enjoy the locals. There are rainforest walks or you can just lie on the beach and soak up the sun. Watch out for stingers in the water during the months of November to February. You may find that the beaches are closed during this time. This area is a must if coming to northern Queensland.