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.

thenbrent

Every time a page reloads to submit a form, a puppy dies. This plugin is the saviour of puppies.
Grunion Ajax submits a <a href="https://wordpress.org/extend/plugins/grunion-contact-form/" rel="ugc">Grunion Contact Form</a> using Ajax. It makes it super fast for visitors to submit a form.
The Grunion Ajax Javascript file is only loaded if the post or page in question includes the Grunion <code>[contact-form]</code> shortcode, so it’s efficient too.
The only caveat, Ajax submission has not been tested for Grunion Forms included in a widget.

Grunion Ajax

Using Grunion Contact Form? Make form submission slick with Grunion Ajax.

Simple AJAX Form vs Grunion Ajax