Mark Jaquith

When your posts get a lot of comments, performance can be a concern. The generation of the comment HTML and the delivery of all that HTML can slow down your page loads. This plugin has pages load without comments, and then uses a secondary AJAX request to pull down the comments. Navigating through the pages of comments is also handled via AJAX. On my test install with 100 comments per page, the <code>onload</code> event fires 2x faster. The HTML is generated by the server 6x faster. The HTML downloads 3x faster. The uncompressed size of the HTML is reduced by a factor of 17.
Initial development of this plugin was commissioned by Google — many thanks!

AJAX Comment Loading

Loads comments with a secondary AJAX request, including comment paging. Speeds initial loading of the page.

AspieSoft

Easily lazy load another page simply by adding a shortcode with its url.
The 2nd page wont load until the user scrolls to the bottom, than an ajax request is sent to get the page content. 
This can help speed up large pages on your site, by not loading the stuff users don’t see until they scroll down closer to the bottom.

AspieSoft Ajax Load Page

Easily lazy load another page simply by adding a shortcode with its url.

AJAX Comment Loading vs AspieSoft Ajax Load Page