highlightTextarea is a jQuery plugin which allows you to highlight words and sentences inside of <textarea> and <input> elements. Words are defined in a jQuery array and you can customize highlight color and case sensitivity. The highlighting updates itself when typing in the <textarea> and follows scroll and resizing (with jQuery-UI).
http://garysieling.github.io/jquery-highlighttextarea/
3.1.3: Support text ranges with HTML entities
3.1.2: Added tests for jQuery versions & verify on jQuery 1.5+
