Like Button

Leonardo,
The best way to do what you're looking for is to simply include the Like module somewhere on your page with a link to your Fan Page. I honestly wouldn't recommend a Like button at the bottom of every article that really references your Fan Page. That will confuse users and would only get you one Like when you could get more. More Like's improves your site's social status and also pushes Like's into the user's feed more often.. as well as with relevant content (the article that may have really interested a user) and not just your Fan Page.

In short, you can have more than one Like button on a page. However, if you only want one on (every) page, the JFBCLike module is likely what you want.

I hope that helps,
Alex