Ubuntu :: Act Upon The Existence Of A New File?

I have a cron job running to act upon files if they exist in a folder... the problem is the nature of those new files. New files aren't put there very often, the server isn't used much (most of the time) so I would like to not check every minute to see if a new file is there and allow the disks to spin down and go to sleep. However, when a new file does exist there, it needs to be acted upon ASAP.

So currently I'm handling that with a cron job... it works... but what would work much better is the ability to act upon the event of a new file being present. Is there a way to trigger action upon new file system activity in a certain path? or just keep doing what I'm doing and have the system check all the time and keep the disks awake just in case something shows up?