What is your budget for the hotel?

As for things to see, unless you are into that kind of things, skip Sentosa which is an artificial disneyland kind of place. See here what Singapore has to offer:
http://www.molon.de/galleries/Singapore/

It sounds like you like theme park places, but some more traditional activities that I like are
The Orchid Garden inside the National Botanic gardens
The Singapore Zoo or the Night Zoo,
The Asian Civilizations museum
Wander in Chinatown, Little India or Arab Street
A food tour such as this one with Betel Box: http://www.betelbox.com/tour-food.htm

amln: My budget would be SD300 & below for the hotel (2 nights). Probably, I will look for the hotel again at Booking.com. As for suggestions of places, thanks for your advise. Maybe I will skip the Sentosa Island for next time.

Icuy: Your suggestions are appreciated. Might go to all the places & exclude the theme park in my itinerary.

I would. There is so much real stuff to see in Singapore. Save the theme park & Sentosa for a future visit.

I don't know anything about the Marrison Hotel, but it seems to be in a decent neighborhood. Another great budget choice is the YMCA at One Orchard road, right across from the Dhoby Ghat MRT station. Not sure about current rates, but it is a nice place to stay.

Though the taxis there are reasonable, and the city is small, being close to a subway (MRT) station makes Singapore much easier to get around.

hi Icuy, you are right. for theme parks, i save them for next trip with bigger group. since it will be only the 2 of us, i rather to spend my time traditionally as you said it. I think ut will be no problem at all to get around and I look forward to it. Thanks again for the advise.

I like the Inn at Temple Street in Chinatown. Good location, very helpful staff, attractive rooms with some atmosphere.

hi Mmeperdu, thank u for the suggestion. I have booked Marrison Hotel for this trip. maybe for next time!

Totally agree with Icuy's recommendations, although we did not get to the food tour. The NIght Safari was a wonderful surprise. If you are in the area anyway, the light show was fun:
LOCATION
EVENT PLAZA AT THE PROMENADE
SHOWTIMES:
SUNDAY-THURSDAY:8PM, 9:30PM
FRIDAY, SATURDAY:8PM, 9:30PM, 11PM
WONDER FULL IS SHOWN NIGHTLY, WEATHER PERMITTING. DURATION IS 15 MINUTES.