Plugins page inside CP Settings not working I get an error when trying to access CP/Settings/Plugins: 

Fatal error: Class 'Craft\PluginVariable' not found in folderpath/craft/app/variables/PluginsVariable.php on line 47

Any Ideas?
Sounds like an FTP upload or an unzipping operation didn't finish properly.

Try downloading a fresh copy of Craft from http://buildwithcraft.com and replacing the old craft/app folder with the new one.