Indonesia has some of the best scuba diving in the world, and this is a major draw for tourists with places like Bunaken (North Sulawesi) and Wakatobi (Southeastern Sulawesi) known worldwide. While diving off Bali itself is a little mediocre, Nusa Penida and the Gili Islands offer excellent diving.

Indonesia is the premier destination for traveling surfers. The Mentawai Archipelago west of Sumatra features dozens of world class surf spots.

http://wikitravel.org/en/Indonesia