Hide Quick Launch (Left Navigation) in SharePoint 2007 / 2010

Place the below CSS in Content Editor Web Part (or in your CSS / Master Page/etc)

In MOSS 2007:

<style>
.ms-quicklaunch 
  {
    display:none
  }

.ms-navframe 
  {
    display: none
  }
</style>

In SharePoint 2010:

<style type="text/css">
.v4master #s4-leftpanel 
 { 
  display: none 
  }
 .v4master .s4-ca 
  { 
    margin-left: 0px 
   }
</style>

For SharePoint 2013, Use this: Hide Quick Launch Bar in SharePoint 2013