Just got started into biking as part of my fitness revival (from zero to hero). The problem of biking in Malaysia is that there are not that many shops over there. Even in PJ itself Icould only count about 2-3 shops only, ok more if you consider branches. In Singapore I could find just about one everywhere and most of them are well stocked. Priority here this time is not to replace anythin Ialready have in KL (Basically, the full working bike, my Felt F1X, hand pump, spare tube, saddle bag) but to get the rest of the important accessories. A shop next to Lavender Station in Singapore called Soon Watt distributes quite a good selection of Topeak accessories. The quality is generally good and it's quite reasonably priced. Bought a foldable stand, front LED lights and rear red lights from them.
Got myself a helmet as well, but this is a little more difficult to purchase. You need to find one that fits well. Bought mine from Bike Haus along Bukit Timah Rd, but I finally found out that that shop was at least 10% more expensive than another shop I passed by a few days later. Maybe its to pay for the airconditioning. So my rule of thumb... aircon more expensive. Got a reasonable deal on the Polar Cadence Sensor though. This sensor goes to your pedal, and it senses how many turns of the pedal you'll have in your riding session. Goes along with my Polar S625X watch.
Treknology3 in Holland Grove is another well stocked shop. Sells a lot of Trek and Nike gears. They seem to have the whole range of TReks, and the clothing are quite well stocked as well. The prices are fixed though. AT least with me around.