I got tired of copy-pasting AppleScripts I found online into the AppleScript Editor, so I made a simple Automator Service to do it for me.
Just launch Automator, choose new service (that receives text), add the Run AppleScript action and replace the script body with this:
on run {input, parameters}
tell application "AppleScript Editor"
activate
if contents of document 1 is "" then
set contents of document 1 to (input as string)
else
make new document with properties {contents:(input as string)}
end if
end tell
return input
end run
Activate it under System Preferences » Keyboard » Keyboard Shortcuts » Services » Text » "New AppleScript Document with selection" if it does not show up in the contextual menu when you have selected some text.
[crarko adds: I tested this, and it works as described. If you have the Developer Tools installed it has a Service called Development » Make New AppleScript that does the same thing. It is disable by default so you'd need to turn it on using the Keyboard System Pref as described above. This hint provides a customizable alternative.]

