The SG sales is on-going now, should be able to find lots of good deals. Clothes are a lot cheaper in SG than M'sia during their sales. Personally, I like to buy clothes from Bugis pasar malam. Nice clothes at cheap prices all year long and can haggle the prices too. Make your way to ChinaTown too if you like nice cheap stuff.
For sight seeing, check out the Merlion Park, Esplanade, Sentosa, Boat Quay, Clark Quay, and go to Chjimes at night for the excellent food. For cheaper food, go to Lao Pah Sat ("old market" in Hokkien dialect) which is a food court. Drop by Far East Square for a Bangsar-like experience.
If you wanna buy electronics stuff, go to Sim Lim and bargain away. Don't forget to claim your GST refund too if you purchase electronics.