Flight deals to SE Asia? (Hong Kong)

Hello everyone,
Greetings! My husband and I are new to Hong Kong -- we love it so far! We're planning a little trip ( Protected content ) to somewhere in SE Asia (Thailand and/or Vietnam and/or Cambodia and/or Laos) and we have no idea where to begin looking for good cheap flights. I would welcome any recommendations for good airlines or websites to check out -- also any suggestions for specific places to go!
Thanks so much,
Meaghan