One of the world's greatest natural wonders may be the Great Barrier Reef. The reef streches along most of the coast of Queensland, Australia. It varies in distance from shore from only 50km to over 300 km. It is the largest structure made my living creatures and is home to thousands of extoic fish and sealife, coral and plants. All around the reef lie islands of various size and habitat. Some of the islands are typical tourist spots with hotels and resorts, while others offer the true ecotourist a reason to visit. Many different species of animals and plants live on the islands, including a few wallabies and koalas. No matter which island you choose, great diving is a sure bet. The reef is great for all types of activities including camping, hiking, surfing, fishing. From July through October, whales enjoy the warm reef waters making whale watching a popular pastime.
Heron Island is one of the reef's ecotourist centers. Heron offers seminars and lectures to tourists who want to learn all about their surroundings. To check out more on Australia's Great Barrier Reef, visit the Lonely Planet site. Or check out Barrier Reef and Eco-tourism
The Outback is definatley for the adventuresome. Full of unusual animals and surprisingly great plantlife. This remote desert like environment is largely untouched because of the rugged terrian and unpredictable weather. Australia has a wet and a dry season, the storms are awesome, but could leave you stranded for weeks. You don't want to go in the severe heat of summer either, even the kangaroos hide from the sun! 
Make sure you plan your trip carefully and carry appropriate gear. A four wheel dry vehicle is mandatory for most of the outback. These red dirt roads can take you across Australia in surprisly good condition. Yet a 4WD with extra gas is a must. Camping and hiking are great here an you can go with a guide or solo. Meet aborigines and see Ayers Rock. Although these are some populare things to see, there are plenty of desert treasures to behold. There are several different routes to take and Lonely Planet can show them to you. You may also want to contact the Australian Embassy for more information and travel tips.