Chiang Mai, Thailand
One reason that many people flock to Chiang Mai in northern Thailand is the moderate weather, but the days in April are scorching even if the nights are on the mild side. If you come here from Bangkok you'll really enjoy the cooler evenings, and it's a great chance to visit one of the huge night markets here in Chiang Mai.
April is the first month of the year when Bali isn't having its rainy season, so it's a nice time to come before the crowds start rolling in in June. You might get some rain, but nothing like what you'd see in the months prior, and the storms tend to be quick.
You might think Singapore is a bit rainy in April. That is true, but it's almost on the equator and Singapore is wet pretty much the whole year. Since the quick rain storms can come at any time, this rich and extremely well organized island has learned to deal with them so well that they never become a problem.
Luang Prabang, Laos
If you have ever wondered what Laos is like, Luang Prabang is the best place to experience it. The capital city of Vientiane is pretty underwhelming, but Luang Prabang is one of the favorite stops of experienced travelers to this region.
If you are doing a southeast Asia tour in April you should seriously consider adding Hanoi to the list. The temperatures are actually quite mild even during the day because of its northern latitude. Hanoi is also wonderfully cheap and a fascinating stop as well.
Hong Kong is very rainy all summer, but in April the wet stuff isn't nearly as bad so it's the best warm month of the year for a visit. This city is booming in almost every way, so if you haven't visited in a while you might barely recognize it.
Hotels in Hong Kong are quite expensive by Asian standards, but unlike Singapore, it's possible to find decent deals in good locations if you look around a bit. Food in Hong Kong is an amazing treat, and you can eat for very little if you follow the local workers into the noodle shops instead of the other tourists into the trendy places.
Boracay Island, Philippines
April is another near-perfect weather month in the lovely little island of Boracay. If you are fed up with concrete blocks and chain hotels on so many of Asia's beaches, Boracay is what you are looking for. This place still feels like an old school resort island where no one wears shoes and there are barely any cars on the whole island.