MoniDIR 2000 is a free folder monitoring software that can track file additions, deletions and changes made to folders on your computer. The program allows a maximum on 20 folders to be monitored at the same time.
Whenever any changes are made to these folders a screen will notify the user of the change that was made. It can also play a wav file or email you the notification.
The program is very compact only 550kb. It stays in the system tray and only starts when you have set a time interval for the software to check the folder.
In case you need to monitor files on the network you can check out Directory Monitor.