Are you a veggie?
If not, you need to find a Bee Cheng Hiang (there are loads) and check out their BBQ pork. This is absolutely fantastic - I used to bring loads home to UK before they banned food imports
http://www.bch.com.sg/primary_brand.htm
(Hmm, don't know why my recommendations are food related!)
Also check out the Japanese department store Takashimaya on Orchard road - and the food court in the basement. Really cool and different stuff.
Singapore MRT (Rapid transit trains) are really good, but with the amount of time you're there you should just take taxis - they're cheap.
Go to the top of the Swissotel / Stamford. It's the tallest building in Singapore and you get a fantastic view over the cricket pitches to Clark Quay etc. I stayed there last time on the 23rd floor, and the view was fantastic.