Jeff Waugh

Automagically link Twitterish “@name:” replies in comments.
Note: It hasn’t been tested on versions earlier than 2.1, but may very well work.

@reply

Automagically link Twitterish "@name:" replies in comments.

paul1999

This plugin allows you to specify a default text for the “quick reply” feature in WordPress 2.8+.
The template can contain the comment author’s fullname, first name, link to the original comment and any other characters, spaces, symbols etc.
<h3>Credits</h3>
Matt Wiebe for javascript code.
Kaspars for adding the comment ID tag.

Quick Reply Template Plugin

Allows you to specify a reply template for the quick reply feature in Wordpress 2.9+.

@reply vs Quick Reply Template Plugin