If you liked Vietnam, perhaps try Thailand? Areas like Phuket look really nice, but beware of political instability.
Malaysia also looks interesting, and there's a spectacular looking Marriott located in a national park (it's only a category 2)! Indonesia looks equally impressive too.
I'd recommend Japan because it's very different with a wide variety of experiences from enormous metropolises to pristine countryside.
That is tough, danferrario , so many cool places to explore! I'm really intrigued by Myanmar, I would love to go someday. Last I heard you still needed to book guided group trips into the country, but that could have changed.
I've never been, but I hear a lot of great things about Chang Mai, Thailand, a mountain town that's supposed to be stunning. Thailand's supposed to have great beach towns too, but they're probably pretty touristy.
You have to get a visa for Burma. Looking at the State Dept. website: Burma (Myanmar) it appears you can actually apply for it online and then you have to use it within three months.
It also says that you can go to the tourist areas with no problem, but special permission may be needed to go to other parts of the country. And, I do think parts are off limits altogether.