Not a plugin that I know of, but you can do it pretty easily.
Create a php file with an array with the different sentences and then call that file at the appropriate place in the template.
You’d create a file, for example, called commentremark.php and upload it to your active theme directory that would be something like this:
<?
// Random HTML Generator
// HTML Array....
$mHTML[0] = 'wrote';
$mHTML[1] = 'bloviated';
$mHTML[2] = 'pontificated';
$mHTML[3] = 'thought';
$mHTML[4] = 'expressed the opinion that';
// Calculate index
$iUpper = sizeof($mHTML) - 1;
$iLower = 0;
$iIndex = rand($iLower, $iUpper);
// Display HTML
echo $mHTML[$iIndex];
?>
Then in the appropriate place in your comments template you’ll put:
<? include('commentremark.php'); ?>
