With the introduction of Mac OS X 10.6 Applescript gained access to the Cocoa Frameworks, unfortunately there is very little information available on how to leverage this new found capability.
“AppleScriptObjC Explored by Shane Stanley is the most advanced, thorough, and in-depth documentation for the creation of AppleScript Objective-C applications. Utilizing a hands-on approach, the book guides you step-by-step through the process of integrating the power of Cocoa into your AppleScript applets and applications, demonstrating each concept and technique in fully editable and annotated example projects.”
At $US29.95 this is essential reading for anyone looking to use Applescript to build applications under Mac OS X.
I’ve also added this to the Applescript Resources.