That is a long trip, so you will have alot time to visit. You should visit Indochina area includes Vietnam (my homeland ), Lao, Cambodia. and also can't skip Thailand, malaysia...
This area has a lot of interesting things to discover.
Welcome to Vietnam and have a good trip!
Cheers - that's about the same figure I've budgeted for flights. Good to know I'm in the right ballpark.
One suggestion I would offer when you're in the Vegas area - just a few hours northeast of Vegas are the Utah National Parks (Bryce, Zion, Capital Reef, Arches, and Canyonlands). My personal opinion is that these parks are more interesting to visit than the Grand Canyon. Temperatures will still be quite warm in the summer/autumn (I was there in early October and daytime high reached 38C, but cooled considerably in the evening). A few hours south of Canyonlands is Monument Valley - where a lot of American westerns were filmed in the 60's, but even if you're not a fan of the genre, the country is quite striking.
Also, if you're going to be visiting a number of national parks in the US, buy a National Parks permit (at the first park you visit), rather than a park permit for each park - the National Parks permit allows you entry into all parks and is good for one year (will save a fair bit of money if you're visiting multiple national parks across the country)