Word Highlighter is a WordPress plugin by Sandeep Kumar that allows you to highlight important word(s) on your posts or pages. Ability to make it bold, italic, underline , change background color, foreground color for the highlighted word. Multiple words support.
Using different types of text decorations for keywords like making them bold, italicized or underlining them, gives emphasis to the words and makes them more important for the search engine splicers like google mostly. Using this plugins, you can go one step ahead to boast up your rankings for highlighted keywords in this tough competition world.
Download and info: http://wordpress.org/extend/plugins/word-highlighter/