Twitter is the way to go! Every other person that you know tweets and what better way to interact with your blog/website visitors than letting them tweet their thoughts? If you think that is a lot of work, think again!
Jotabl is a web application that lets you embed Twitter based shoutboxes anywhere on the web. Simply sign in to Jotabl with your Twitter account and specify the URL of your website. Jotabl will provide you with a small HTML code that you can paste anywhere on your website to have the shout box. Simple as that!
If you want more options, you can customize the look of your shout box and set it to filter swear words. When somebody visits your website, all they need to do is sign in with their Twitter account and they are all set to post a message on the Shout box. You can also block any notorious users from using your shout box by signing in to your account at Jotabl.