going to Singapore, Taiwan, Thailand, Vietnam, Xiamen (China) and Hongkong?

Looks like you are visiting the vast region of far east which looks hectic to me. Well, you have to state what is your

interest as its hard to define the must sees, since you want to go to so many countries. And also where are u from and where have u been to? I or somebody else here can help you if you give more details.

Additional details:

From your additional details, here are the recommendation I can give to you.

Singapore: Must See- Singapore Discovery Centre, The NEWater visitor centre, The Singapore Flyer, National Museum of Singapore, The Red Dot Museum of Design and much more. Places to Shop: The newly revamp HDB Hub in Toa Payoh Central is a very good place for you to shop till you drop and the items are not expensive. Vivo City is another newly open shopping centre that you can visit too. Alternative place to stay: stay clear of Geylang and Little India area for safe and clean accomodation. The Coasta Sand Resort is a chalet that is both clean and safe and its located at Pasir Ris, East Coast and Sentosa respectively.

Taiwan: Must See: The aborigines of course. They are located at the eastern side of Taiwan and their cultures are not to be miss. Taipei is the first and number 1 place for you since you never been to Taiwan. Danshui, Yangmingshan and Peitou areas are the few areas that you must go to. Places to Shop: The Dihua Street in Taipei is the place where you can buy cheap and good quality Taiwanese goods that locals visit. The Taipei Main Station underground mall has also lots of shops for you to visit. Alternative Place to stay: Taipei House Hostel, clean and safe alternative to hotels. YMCA Jiantan Youth Activity Centre is another better option. Farm stays is a must for outside Taipei and also homestay in aborigines home.

Thailand: Must See: The transexual (Thai Girls) shows in Thailand is the must see for all visitors. Zoos in Thailand are also a must. Visit Chiang Mai for its arts and crafts and the Death Railway in Kanchanaburi Province is a must go. Place to shop: The BMK is the most famous shops in Bangkok. The floating market is another place for you to shop. Alternative places to stay: I think if you can, try homestays if you can find one. Hostels is another option, but not as good as homestays.

Hong Kong: Must See: The Buddha statue in Lantau Island, Avenue of the Stars, Old Hakka villages and houses, Hong Kong Cultural Museum, Coastal Defence Museum of Hong Kong, The Peak and Kowloon Walled City Park. The newly open Hong Kong Discovery Centre is worth a look too and as the HK correctional museum at Stanley Prison, which is on its 5th anniversary this year. Disneyland is only if you have kids in tow, or else, just miss it. Since you have been to Hong Kong, you should know the other details, but here is my recommendation if you want to know: Place to Shop: Mong Kok for electronic, sporting goods, pets and flowers. Dickson Warehouse & South Horizon Plaza, Ap Lei Chau for fashion and accessories, Midlevels for antiques & memorable items and Sham Shui Po for makeups and clothing accessories. Alternative Places to stay: Not much, due to the markets towards hotels stays in Hong Kong. Hostels is the only other options for clean and safe stays. The another alternative is to rent a room in an apartment in Hong Kong.

As for Xiamen and Vietnam, I had never been to so I can't give you any advice for it. Those are the places you can visit for a short 5 days. Hope the above really solve your planning problem. Hope you have a nice trip ahead of you.