# Enable Rewrite Engine
RewriteEngine on

#Create friendly URL
RewriteRule ^site$ site.html [L]

bzw:

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html
# Replace html with your file extension, eg: php, htm, asp

für php dann eben so:

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteRule ^(.*)$ $1.php