Apart from the view of the city from the Marina Bays Sands Sky Park and the dizzying height of 1 Altitude Bar at One Raffles Place, there is one unexploited (well, unexploited by tourists) place in Singapore with a breathtaking view of the city's skyline: the Marina Barrage.
It is actually a dam with a park on it's rooftop. On any given day, it is a regular park full of families and youths having picnic and flying their kites. But I would think it's best to go there at night where you can see the city lights from afar.
Photo from http://news.gov.sg
Yes, the Singapore Flyer, Marina Bay Sands and Singapore CBD-in all it's illuminated glory-is viewable from the 'roof park'. The lighted kites flying, the barrage of stars, accompanied by a perfectly round moon seem divine and yet unearthly as you stare at them. You can lie on the grass, soak in the view, spend QT with friends or that special someone all the night through as it's open twenty-four hours (I think!). Marina Barrage is one of the best and special places in Singapore that I've ever been to. Apart from the view and the place, it's the companion that made my visit here extraordinary. :)
Getting there: Best by taxi! Otherwise, you would have to catch the Bus #400 or a shuttle bus from the Marina Bay MRT Station (Red Line). It's hard to get out from here at night though, be warned!