Luko's list is pretty good although I am not a fan of Vietnam.
Some more ideas within Indonesia - that giant island called Sumatra has some amazing things to see. Catch an early morning flight from DPS to Jakarta then a two or three hour wait from memory to connect to Padang - Minangkabau - and spend a few days on Cubadak island and dive the Indian Ocean. You can also head out to the Mentawai islands which are generally surf destinations but are also lovely islands with some people still living their ancient cultural ways - you can get their using the Ambu Ambu ferry that departs from Padang harbour. If you hit Cubadak the owners of the resort will organise transport to and from the airport. There are a few ''living bridges'' trained out of trees on the mainland near the port worth checking out.
Lake Maninjua and Lake Singkarak are both beautiful, the second being the largest in West Sumatra.
Pasaman is the next regency in West Sumatra and while relatively unknown it is absolutely beautiful and gave me sightings of wild orangs and wild pygmy elephants.
The Gunung Leusur or Bukit Barasan Selat national parks may save you wandering around the jungle looking for things - btw there are 580 species of birds in Sumatra so you should get some birding in there

While still in Sumatra...try and head up to Lake Toba an beautiful volcanic crater lake. You have Samisir Island inside a lake inside the island of Sumatra and the fantastic Sumatran architecture which is similar to that found in Tana Toraja in Sulawesi is very interesting.
I last went from Padang to Lake Toba/Parapat by bus which I believe is still running the trans Sumatran highway but book the bus in advance or you can fly from Medan.
Just touching on West Sumatra here, also North Sumatra and Medan are interesting.
If Palau Weh catches your interest and you want to dive Palau Weh you will need to enter Aceh province by air - I have always used Lion Air and am still alive.
You could probably spend 5 years exploring Sumatra alone. Just dont go to Bangka Bilitung in Sumatra instead of Bangka Sulawesi Utara....one is a great dive spot the other is a sulfur mine and not pretty at all.