tempranova

This is a simple plugin that uses AJAX to load comments, converting the “Newer/Older Comments” button into a button that loads more comments instantly.
This plugin also paginates nested replies. You can customize styling in whatever way you choose.
Using Settings > Comment Load More, user can set desired pagination (currently both comments and replies have the same number).

Comment Load More

This plugin allows you to load more comments instantly via a button push (AJAX), instead of pagination that reloads the page.

Mark Jaquith

Michael Adams (mdawaffe)

Other preview plugins don’t know what sort of changes WordPress will make to a 
visitor’s comment, but this plugin uses AJAX and other buzzwords to send each 
previewed comment through WordPress’ inner voodoo.
The result? With the click of a button, your site’s visitors can preview their 
comments exactly as they will appear when they submit them for realies.
Requires PHP5.

Ajax Comment Preview

Visitors to your site can preview their comments with a click of a button.

Comment Load More vs Ajax Comment Preview