Every night at 8 pm and 9 pm there is a nice lightshow at the Matina Bay Sands area where the hotel and it's surroundings are lit up with lasers and colorful combinations. There are quite a few locations from where you can get a nice view of this spectacle. First there is the area at the foor of the MBS where you clearly have the best view for the projections in the water, but you will miss the spectaculair lasers, because they are pointed from the hotel.
Second is the view from the other side of the bay where the Merlion is of the spot next to Esplanade Theatres. From there you have beautiful photo opportunities.
Make sure if you want to have a nice spot to settle yourself a bit early.
The show changes every now and then so if you come back in Singapore after a while it is worth to plan a new visit.

My first time catching the show (it's freee!) as I was being a tour guide to some friends from overseas.
It was a wonderful experience, for both myself and my friends. The show combined lights, waters, and music, and made use of projectors to form beautiful visual images as well. Pretty sure there's a story line to it, but we couldn't catch it...
We were able to find an area to sit in front of the displays (bridge in front of The Shoppe) as we arrived 20 mins earlier before the 9pm show. Was a little drenched since we were right in front but twas refreshing =p
All in all, an enjoyable show to end the day with!