I use Cocoatech's Path Finder as my primary file browser, reverting to the Finder only on rare occasions. Sometimes, though, I'll open a window (and navigate into some folder) in the Finder by force of (20 year) habit. I wanted a simple way to open that same folder in Path Finder, so I wouldn't have to navigate to it twice.
After some Googling, I stumbled on the solution in this forum thread on the Cocoatech forums. User maaku posted this very handy AppleScript:
on run
tell application "Finder"
activate
set this_folder to (the target of the front window) as alias
close the front window
end tell
tell application "Path Finder"
activate
open this_folder
end tell
end run
Copy and paste that code into Script Editor, then save it as an application (File Format » Application in the Save dialog) in a convenient spot. Then drag the app to the Finder's toolbar or sidebar; I put mine on the toolbar.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090424063955133