Getting Rid of the WordPress.com Toolbar on Other Sites?

Add the following code to your user stylesheet:

#wpcombar
{
    height:         2px     !important;
    overflow:       hidden  !important;
}
#wpcombar:hover,
#wpcombar:focus
{
    height:         28px    !important;
}

This will shrink down the toolbar to a 2px line. You may use display:none to remove it completely, but then it will not be accessible when you need it.