If you don't want to venture out of the airport, there's always the Crowne Hotel.

Otherwise, there's Marina Bay Sands, the latest SIN icon with the SkyPark and the amenities of the Orchard Road shopping belt nearby.

There's of course Raffles Hotel, the grand old dame where you can will time away with a Singapore Sling.

For a more "relaxed" feel away from the city buzz, try Capella Hotel. It's on Sentosa island (about 20-30 mins away from the airport) and there are plenty of sightseeing opportunities on the island itself.

If you prefer city sights, MBS is the way to go; if you're a beach person/ prefer more historical sights / prefer things to do (like simulated skydiving), then Capella is it.