In OS X’s Script Editor there’s a navigation bar that makes it easy to get around your script, allowing you to jump directly to any declaration. Under the “View” menu, choose “Show Navigation Bar” to reveal this tool between the script view and the toolbar. Also on the bar is a language chooser (should you happen to have another OSA language like Javascript installed).
This feature is also available in the script editors Smile and Script Debugger, and allows jumping to script objects, handlers, globals and properties in your script.
More info about Script Editor’s Navigation Bar, at Apple’s AppleScript Site.