I posted this link today in another forum and thought it may be best noted here as well.

www.airasiaplus.com

It's a 3rd party site that searches a 15 day range for the route & date selected and shows lowest prices for each day. ^

Once the best day is found, you have to return to the real Air Asia website to ticket. Kinda like expertflyer for Air Asia. I love it.

enjoy,
stp