For sunrise (Been there and seen it, recommended):
Merlion Park, Esplanade Bridge, Esplanade Theatres, Benjamin
Sheares Bridge (entry from Ritz-Carlton there) and Marina South
(open fields).
See the sunrise, it is romantic.
Look at the skyscrapers, it is tinted orange.
The SIngapore River is gold.
But all only in GOOD WEATHER CONDITIONS. 
