United is the other alternative, but they have one of the worst timings and ex-HKG is a bit vunerable to delays since 744s arrive from the US. Fares ex-HKG on
www.unitedairlines.com.hk go as low as HKD900 rt (SGD162) regularly but for some reason,
www.unitedairlines.com.sg ex-SIN is significantly more expensive (SGD538).
By order of price (published fares on website) - full-service carriers:
Singapore Airlines
Cathay Pacific
United Airlines
Jetstar and Tiger are both very competitive. Maybe even consider AirAsia to KUL.