Tori Ajax is a WordPress plugin that allows you to easily add Ajax code to your WordPress with a few lines of code.
Setting up Ajax in WordPress can be a headache, especially when you want to add multiple Ajax endpoints. Tori Ajax eases this process by creating a single function (toria_add_ajax()) that allows you to add Ajax endpoints using the toria_add_ajax() function hence saving time. Also, it makes the management of your code easier since you only have to deal with just the toria_add_ajax() function instead of multiple WordPress functions.
The plugin also has a couple of filters that allow you to filter/modify the ajax variables in your setup.
Please check out the Ajax documentation to get started.