Pretty little liars came out when?

Pretty Little Liars - 10/3/06
Flawless - 3/27/07
Perfect - 8/21/07
Unbelievable - 5/27/08
Wicked - 11/25/08
Killer - 6/30/09
Heartless - 1/19/10
Wanted - ?/?/?

Courtesy of http://www.myspace.com/prettylittleliarsss