O&O DiskStat Sidebar Gadget is a free gadget for the Windows Vista Sidebar or the Google Desktop Sidebar (5.5 and above). It allows you to monitor drive space, disk activity, temperature, and health at one glance. Features include:

• Animated disk activity indicator
• Pie-chart-style drive space display
• Health status indicator
• Temperature indicator (requires Sidebar elevation on Windows Vista)
• Verbose display in flyout
• Two themes:
  • BlakPlex, blends well with Aero desktop theme
  • Klassik, blends well with Windows Classic desktop theme

Drive space, disk activity, health status, and temperature are colored according to their current value. Green indicates an ok status, orange denotes an above normal value, and red points out a possible condition of failure or performance loss. For temperature values, color codes were chosen based on a long-term study by Google.