PHP
Command to run a PHP5 cron job:
php /home/user_name123/public_html/cron.php
Optional flag sometimes required for a PHP cron job:
php -q /home/user_name123/public_html/cron.php
Command to run a PHP4 cron job:
/usr/local/php4/bin/php /home/user_name123/public_html/cron.php
More
Command to GET a remote file:
/usr/bin/GET http://www.some-domain.com/file.php
Command to run a CGI cron job:
perl /home/user_name123/public_html/cgi-bin/file.pl