Last December I put together a list of Sysinternals tools that I found the most useful. Recently, I have been looking through the entire list and found a few more tools that you might keep on a flash drive, just in case the need arises.
The first utility on my new list is DiskMon, which looks at all of your hard disk traffic and reports it to the screen. When the window is displayed, the default is to auto scroll the data constantly filling the window as you use your PC. If you minimize the application to the tray (Options | Minimize to tray disk light) DiskMon will blink as it monitors traffic.