I accidentally deleted the Show Desktop icon which sits normally on the bottom left hand corner of the Taskbar. How do I restore the icon?

Click Start, Run and type the following command:

regsvr32 /n /i:U shell32.dll

The Show Desktop icon file should be available now.
or
Click Start, Run, and type Notepad.exe. Copy the following contents to Notepad.
[Shell]Command=2IconFile=explorer.exe,3[Taskbar]Command=ToggleDesktop

Save the file as - : Show Desktop.scf. Now, drag the file to the Quick Launch Toolbar. (Notepad might automatically append a .txt extension to the file name. Remove this extension if present.)