How to add a Safari toolbar button that runs an AppleScript How do I add a button to the Safari toolbar that, when clicked, executes a given AppleScript?
Another solution, and this is really dependant on what you want to do, is to use Services to execute your Applescript.

It doesn't create a toolbar icon, but will allow you to create a service from your AppleScript. You can then define a shortcut key in the System Preferences Keyboard Services pane

This page over at automatedworkflows.com shows an example as well as a link to the rather useful ThisService program.