KL
Can recomend The Boulevard hotel, located at Mid Valley Mall, also there is The Garden Residence and Cititel in the same area, Mid Valley Mall and Garden Mall are linked by a foodcourt in the basement and I believe the two combined make the largest Mall in Asia. The LRT/Komuter Train can be reached on foot and can take you anywhere quite quickly and cheaply, if a little squashed at peak times, or you get cabs easily enough to KLCC etc.
The Sunway Resort is also good as I believe is the Sunway Pyramid if you want the water park and the Sunway Mall (adjacent).

Singapore
The Orchard Hotel is good as is the Marriot, both are in Orchard Road main shopping area and both within easy access to LRT and buses. Again depends on budget, the cost is high.

All the above however depends on budget try Agoda for other ideas.