Let me kick off this useful thread, as mooted by Kenneth.
A good place to check is -- http://www.airfares.com.sg
Get a bargain fare out of SIN, then just add on a cheap KUL/SIN hop.
Good promo fares out of KUL are usually offered by Qatar, Emirates and Etihad.
Go to their websites, and subscribe to their newsletters. You'll get informed of such promos, which can happen several times a year.
Qatar likes to offer really low fares for new destinations, so watch out for those new launches.
Edited by Naim, 31 January 2013 - 12:10 PM.