Viewing all the cron jobs running on your system can be very useful. This command (which I found on Stack Overflow, thanks to Jørgen) outputs all the jobs to the screen for you.

tail -n 1000 /var/spool/cron/*

I find this particularly useful when making sure all my Magento sites are running the correct cron jobs at the correct intervals.

If you have more that a 1000 cron jobs you can update the number to display more.