TagInput

This plugin is very simple and easy to integrate.

html code:
<script src="/jquery.min.js" type="text/javascript" ></script>
<link href="plugin.css" type="text/css" rel="stylesheet" >
<script src="plugin.js" type="text/javascript" ></script>
<input class="tagger" name="tags" type="text" value="tags" >

javascript:

$(".tagger").tagInput();

or

$(".tagger").tagInput({class:"tagInput"}); // to append extra class attribute to generated tag box.

This plugin also contains AutoSize plugin.

$(".tagger").autoSize({ comfortZone: 30, // space to type below curser
            minWidth: this.width(),
            maxWidth: 500,
            minHeight: this.height(),
            maxHeight: 500,
        });