Palau
This country in the region of Micronesia was among the first countries to become a shark sanctuary. All shark fishing is prohibited since 2009.

What to see: Mantas, sharks (mainly grey and white tip reef sharks, some hammerheads), eagle rays, friendly napoleon wrasse, big school of fish, mandarin fish, WWII wrecks, a cave and the jellyfish lake

Diving: Either from a liveaboard or land-based with speed boats. The currents are strong with some negative entries and a reef hook is required. The rides to the dive sites can be tough with high waves.

Level: Experienced divers, need to be able to do negative entries, handle a reef hook and have experience with drift dives

Who should go there: Experienced divers who are looking for large pelagics and wreck enthusiasts

How to get there: Flights from Manila, Guam, Yap, Tokyo, Taiwan, Seol and Hong Kong. The flights are generally not cheap and only fly on certain days of the week. When flying through Guam make sure to have your ESTA ready or whatever document you need to enter the US.

Where to stay: It is possible to stay in hotels in Koror on the main island and do day trips or stay on a liveaboard. The cheapest hotel rooms starts at USD 70, a bed in a dormatory is available for USD 35 at Ms. Pinetrees. Best ask your dive shop to assist in booking the accommodation or book a package.

Where to dive: The land based options are Sam’s Tours, Palau Dive Adventures, Fish n’ Fins and Malm Divers. The liveaboard options are Palau Aggressor II, Rock Island Aggressor, S/Y Palau Siren, Solitude One and Ocean Hunter I and II.
Most dive sites can be reached on day trips from Koror. For divers who would like to have a range of restaurant options in the evenings and only want to do 2 or 3 dives per day or are on a budget land-based might be the best option. For dive, sleep, eat, repeat with as many dives as possible per day the liveaboards are the better option.

Rates: Daytrip including two dives costs $120 to $160. The dive shops also offer dive packages and combination packages including accommodation. For example a package for 5 days with 13 dives including Pelileu and jellyfish lake starts at $ 1100 with Palau Dive Adventures. The liveaboard rates are similar for all companies for 7 days $ 3100 to $ 3600 or 10 days for $ 4600 to $ 5100.

Climate: Around 30°C all year round, dry season December to April

Water temperature: 28-30°C

Visibility: Normally amazing visibility of up to 40 m, can drop to 10 m depending on conditions and the dive site

Season: Diving is possible all year round, it rains more between June and August. Typhoon season is June to October. During this time conditions can get rough when a typhoon is passing close by. Some of the famous dive sites might be difficult to reach when the waves are high. More sheltered sites can still be dived.

Favorite dive sites: Blue Corner with schooling fish, turtles, sharks and the most friendly napoleon wrasses / wrecks / Ulong Channel for cruising grey reef sharks and drift through the channel / mantas and sharks at the cleaning station in the German Channel

Update
I have recently (August 2016) heard that the waters were too warm causing the jellyfish to decimate in numbers and the pelagics to stay deeper. This lead to many people not having the best experience in Palau. Before you book your trip try to find up to date information about the recent sights of pelagics and the condition of the jellyfish lake.

My trip:

I flew from Manila to Koror and took a 10-day trip with the Palau Siren. The last minute offer on a chartered trip was $ 2000. The boat was luxurious with probably the best and funniest chef I ever experienced on a liveaboard.
We were unfortunate to have a typhoon passing by in the north which made it difficult to get to the dive sites like Blue Corner. We finally made it to each of those sites at least once and were diving a lot at German Channel and the wrecks. The Siren is a great boat but not too nice in huge waves. We were a bit jealous with the divers on the Aggressor fleet (catamaran) who ankered closer to the sites. We had long rides on the speed boats to the dive sites each time.
I can definitely recommend Siren for a trip outside of typhoon season. If you take a trip between June and November book a trip on a catamaran or land-based.