So, a couple of months ago we saw a deal on ozbargains.com for Jetstar- free flights from KL to Singapore. Totally free! (except we ended up paying $15 for checked baggage).
We duly got four flights for both of us, because our plans were in no way set in cement. Others no doubt did the same because when we ended up taking the flight it was practically empty! It is a budget airline but there was nothing at all bad about the flight, it was on time, comfortable and the service was great.
No idea why Jetstar decided to offer this apparently one off slate of free flights but it just goes to show that it pays to keep up with deals websites like ozbargains.com etc!