For the backpackers heart, Koh Chang is a must. Although the fast development of commercial hotels along its pristine beaches are starting to ruin the islands touch, the island is geared for backpackers experience. Nestled close to Cambodia's border, the island features numerous hidden alleys were backpackers-inns hide away secluded in rocky cliffs adjacent to the pebble-filled beaches. "Bo's Place" comes to mind, an exotic hide-out in the cliffs at the end of White Sands beach, where you really are nothing but nature all around you together with an eat and bar area to socialise with fellow backpackers.
Price wise the island is very affordable, and hasn't been ruttled with foreign inflation like the rest of the country's exotic places (this was 2005).
The beaches are still unspoilt and untouched, whilst a motorbike trip around the island and smooth "mai-thais" (cocktails) along a beach sunset fulfills the islands reputation as mini-paradise.
I fully recommend going.