Vietnam you would want to stick to the middle bit, Hoi An and Hue, not ideal time for N or S
Thailand - not the west coast. East coast like Ko Samui is better - but still hit and miss whether you get good weather with the odd shower or grey skies with more rain
Other suggestions with good weather in August :
Sri Lanka (avoid south and west coasts but east/north should be good)
Malaysia (east coast islands like Perhentian, Redang, Tioman) and Singapore
Borneo
Indonesia: Lombok, Gili islands, Bali, or further afield if you want more off the beaten track
Peru, Ecuador, Bolivia (but not beachy)
Kenya, Tanzania, Botswana
How long have you got?