Sim Lim Tower-- notorious for ripping people off (or these folks are more commonly called "crooks") you can indeed find most things similar to some of the best electronics stores I've ever been to, like You-Do-It or All-Electronics.
There are certain things that are basically impossible to find though, like voltage converters (eg. no 12V DC to 5V), clear-colored single LEDs, or silicone coated stranded copper wire. Everything was cheap by my standards (though you should really haggle for at least 10% less).
BLK. 261 Waterloo Street
#01-25 Waterloo Centre Singapore 180261
It's across the street from the Lasalle school of art.