Windows PowerShell, 124 123 121 119 116 112 chars
$s,$w,$h=-split$input
$(($a=1..$s|%{$x=' '*($s-$_--)
"$x/$(' '*$_)\$x"*$w})
$a|%{-join($_[-$s..($s-1)])*$w})*$h
If we allow the input to span three lines instead of being generally whitespace-separated we can get it down to 109:
$s,$w,$h=@($input)
$(($a=1..$s|%{$x=' '*($s-$_--)
"$x/$(' '*$_)\$x"*$w})
$a|%{-join($_[-$s..($s-1)])*$w})*$h
As arguments to the script (from within PowerShell) it'd be 105 bytes:
$s,$w,$h=$args
$(($a=1..$s|%{$x=' '*($s-$_--)
"$x/$(' '*$_)\$x"*$w})
$a|%{-join($_[-$s..($s-1)])*$w})*$h
This would then be called like this:
PS> .\diamond.ps1 2 2 2
