Difficult with such a short time. Orchard Road is a must if you are into shopping. For something completely different a visit to Changi Prison Museum is a very sobering experience. You could also do the Night Safari. Look on the Viator website for more ideas. A trip on a boat round the harbour is also fun. I'm sure other people will come up with more ideas, but a point to remember is that the heat and especially the humidity can be quite energy sapping so don't overdo it. What you can't see this time you can always put on your 'to do list when I visit Singapore again'!!!!

Rosalyn

a singapore sling at Raffles I love Chinatown as well. Whilst in Chinatown, visit Sri Mariamman Temple.
Eat at a Hawker stall- try Newtons Circus
Give Sentosa Island a miss
I enjoyed Changi prison museum( well enjoy is probably not the best word)but its a bit of a scutter to get to if you have a very limited time.
If you want to get some insight into what happened during the war, the Battle Box was very interesting and its handy for many hotels. Its at Fort Canning Park and can be done in an hour
http://www.visitsingapore.com/publish/stbportal/en/home/what_to_see/world_war_ii_sites/battle_box.html
That Uniquely Singapore Tourist info is very handy.
Which hotel are you staying at?

I would imagine that on the first night in Singapore you will probably be feeling pretty shattered after the long flight and combined with the heat and humidity you may only want to eat and sleep.
The first time I visited Singapore I took a night tour on the first evening, the coach took us around the city, stopped off for a meal at Boat Quay and ended up in the Raffles Hotel where we were served a Singapore Sling, all included in the price of the tour.. You could take a half day city tour on your full day there which would give you an idea of where things are and what you may want to revisit.
If you are staying in Singapore with Singapore Airlines as part of of their Singapore Stopover program you can ride the Singapore Airlines Hop on Hop off bus around the city free of charge, if not you can ride the bus for a small fee
As Babs suggested a bum boat ride round the harbour can be fun and a welcome way of relaxing if the sticky heat gets to you.
I always enjoy my visits to Singapore despite the heat and humidity, it's a great place for a stop over even if only for a couple of nights.

Thanks for the ideas folks, I will be back in Singapore on 3rd Jan for 1 day before returning to Scotland so if I miss anything I can do it then.

Forgot to add I am staying at the Peninsula Excelsior Hotel, I had originally booked Traders but changed to this as it seemed in a better location, nearer the MRT etc.

To be totally honest I don't think the Peninsula/Excelsior comes anywhere near the quality of Traders, though for two nights I guess it's OK due to the location. P/E is just a short walk to the river for Boat and Clarkes Quays where there are lots of restaurants and as you say it's not far from the MRT(With Traders you need to take Taxis to get to places). I stayed there a few years ago as part of the Singapore Airlines Stopover Program and wasn't impressed, but the price was right. I believe there is ongoing renovation at the hotel which is needed as the rooms felt somewhat shabby and outdated though adequate for a short stay.

Boat Quay is a great place for night as there are loads of great restaurants. So your hotel is in a good position. I have stayed at Traders- lovely hotel with a superb, awardwinning restaurant, but a bit of a scutter for getting out and about. If you have only 1 and a half days you are probably better in the hotel you have.

I had a 2 night stopover in Singapore in November - not long enough!!!! But I used the Hippo Hop On Hop Off bus which departs from Suntec. I bought a two day ticket. There were two different routes to take, plus a harbour boat trip, and an evening trip to Sentosa all included in the price of the ticket. I thought it was great value for money, and I was able to see an awful lot! Mind you I think I only had about 6 hours sleep in total I did skip Orchard Road, as I preferred to wander around Chinatown and Little India. I also hopped off the bus and walked for miles when the traffic was at a standstill.

to be honest, I skip Orchard Road as well- unless its the Great Singapore Sale time(July)