TCBarrett

This plugin requires is just the front end javascript library, the following two things to be done in support: 
1. Add the class ‘simpleajaxform’ to your form. 
2. Make sure you have the correct wp_ajax handler hook defined.
It was primarily built as an example for a blog post.

Simple AJAX Form

A simple jQuery javascript library to ajax enable forms.

aposai

Display your archives in collapsible mode using ajax and jQuery.
Each subnode is loaded via ajax as per user request, so not whole archive is loaded each time your archives page is displayed. If you have performance problems or server issues with other archive plugins, try this one and enjoy.
It also displays the post count for each year and for each month and the comment count for each post. And uses your current wordpress date_format to format the dates.

Ajax Archives

Display your archives in collapsible mode using ajax and jQuery.

Simple AJAX Form vs Ajax Archives