O&O DriveLED takes the hard disk LED, which is built into your computer, and puts it right there on your monitor screen.
And there's more - you can see information about activity on virtual drives, e.g. network drives, and you can easily tell the difference between disk reading and disk writing activity.

fxp://ftp.oo-software.de/pub/oodriveled/oodled_1_0_74_english.zip