Support Tickets Center is a WordPress plugin that adds state of the art ticketing support functionality to your website.
responding server slow a bit and it slightly slows done editing of the posts but plugin and support worth 5 stars. Would recommend.
This is the only helpdesk I'll recommend for WordPress , its easy for the clients to use , the backend has all the bells and whistles of the paid help desks and the interface is very easy to use and install.
Also I had an issue where the plug in was not working right , opened a ticket with zengiri and within 48 hours they fixed the problem and put out an updated plugin with the fix.
they are awesome.