A paradise of sparkling water and lush jungle, the island of Pulau Tioman has been historically viewed as one of the most beautiful islands on Earth (early hominids were known to have grunted something along the lines of, "dude, this place is totally awesome"). Pulau Tioman is currently under development as more of a tourist haven, with an expansive marina project underway in the most populated area, Kampung Tekek, that will vastly improve the tourist infrastructure. But for the time being, the island's beaches and forest treks are largely untenanted by the masses and are primed for a truly novel vacation experience.
The better hiking trails follow the power lines between villages, although the ultimate adventures come in the form of coral reef dives off the coast. There are a number of excellent spots and a few different dive centers, so do a little research to see which may fit within your expectation of budget, eco-friendliness, and credibility.
Note:The island is accessible by both plane (form Singapore and Kuala Lumpur) and ferry (Mersing or Tanjung Gemok, near Johor Bahru).