Refresh Finder is a handy AppleScript wrapped in an app. The app's icon is designed to match those in your finder's toolbar. Simply drag it to your toolbar, hold it for a few seconds, and drop it in place.
Download: Refresh Finder 1.4.0.dmg
Update 111125: New version: 1.4.0. Updated for Lion. Thank you Matt Sephton for letting me steal your icon, and Nick Barron for pointing out the need for a Lion version.
Update 090911: New version: 1.3.0. Updated for Snow Leopard. This seems to be the latest version that works on PPC (Thank you Lucas Pestana for pointing that out)
Update 071113: New version: 1.2.3. Now Leopard friendly (if anyone should feel they still need it on Leopard). Thank you Brian Latimer for some great input.
Update 070903: New version: 1.2.2. Fixed a bug where the script fails if one of the Finder windows is an info window. Thanks goes to Lionel Mallet for a neat solution.
One more thing:
Download: Restart Finder 1.1.dmg
Introducing Restart Finder. Based on the same simple concept as Refresh Finder this little button does exactly what it says. Enjoy!