Indonesia, Gili Trawangan

Gili Trawangan is one of the three Gili Islands off the coast of Lombok. Trawangan is the largest of the three islands and has great diving and partying.
It's a long day trip to get there from Kuta in Bali. You can take public transport to the ferry port on Bali's east coast, Padang Bai and take the ferry to Sengiggi on Lombok, then two busses to Bangsal and then a small boat to whichever Gili island you want to get to. This is the cheapest option but lots of hassle. Some taxi drivers in Padang Bai drop you off about 500m from the ferry terminal where people grab your bags and run to the ferry before you have a chance to carry your own bags and then demand a fortune for the service. Bangsal is apparently worse with touts trying to grab packs off the bus. You have to have your wits about you and everyone who we spoke to who had done it said it was a pain.
The other option is to go with Perama who run a minibus to Padang Bai and then their own boat directly to the Gili Islands. On the way back they have a boat to Lombok, bus to Sengiggi and then their own boat back to Padang Bai and a minibus to Kuta. It costs marginally more but saves a lot of hassle. You get snacks and lunch on the boat which even has a beach! We payed 180 000 each one way for the trip. If you book future trips with Perama you get a 10% discount. They also offer boat trips to the Komodo islands and can organise combination bus / ferry trips to many places. We found them very reliable and knowledgable.
You can also fly between Denpassar (Bali) and Mataram (Lombok) with Merpati which is only a 15 minute flight in a tiny plane. Prices are seasonal.
We did a day snorkelling trip around the islands on a glass bottomed boat which was excellent, saw many turtles and fish. The coral here is not great as it's been either bleached, dynamited or blown away in a storm a few years ago. The animal life is excellent though. You can organise the day trip from any of the stalls along the beach.
All the dive shops charge the same price which is $25 per dive plus 30 000 rupiah per person regardless of how many dives you do which goes to the local fisherman as an environmental charge so they don't do dynamite fishing!
We dived with Manta Dive as we had made friends with a DM there but had great info and lots of help finding accommdoation from Steve and Leila at Blue Marlin.
There are parties every night and the restaurant or dive shops take turns hosting them so there's less competition. A few places have barcos which house your own private TV and DVD which you can choose from a selection and watch during dinner.
There are a few market stall supermarkets which all have the same price so you don't have to shop around too much.