Although I've only obtained my Padi Open Water certificate, I've had the good fortune to dive in the following countries:
During these dives, I've seen a vast variety of soft and hard corals; an endless selection of fish of all sizes, shapes and colours; magnificent colourful giant clams; tortoises, stingrays, sea snakes, and reef sharks; and the odd wreck.
Being Australian, I may be biased, but for value for money, I recommend an Australian company which provides, for comparatively reasonable and competitive costs, the convenience of enjoying:
My recommendation is the three day, two night package, providing up to 11 different dives on four sites.
For more details visit the company's great web site: http://www.downunderdive.com.au.
Another exceptional dive location is on the wreck of the Yongala, out from Townsville.
The Yongala was a 109 metre long steel freight steamer, which sank without trace in March 1911, with the loss of all 124 on board. The structurally identifiable wreck was subsequently located in 1958, in 30 metres of water, and now forms a reef for a variety of sea life in a sandy area.
It is probably the most enjoyable dive I've experienced. I was amused to read the article (picture attached) in a Melbourne newspaper not long after my dive.
Go here for web site index, including pictures and comments about other destinations, and other activities.