Note: I no longer recommend this plugin. There is a Facebook “Like” plugin that links directly to a visitor’s facebook page. Click here to view that Recommended Plugin review.
If you’re looking for a simple plugin to allow visitors to click “Like” on your posts without having to sign in, then “WP Likes” is for you. Simply install & use it out of the box, or go to “Settings”, “WP Likes” to customize the look of this plugin. You can change the image as well as the relative CSS styles that position and color the button to match the style of your site.