This should do the trick for you - (put in .htaccess of root folder):
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^(.*)$ $1.php
Remember never to copy directly from browser (or this message) as syntax gets corrupted. Copy and paste into Notepad++ first, check characters, and then paste into .htaccess. This should be ok as it's usually (") and (,) that get corrupted.