For the last few hours I've been pulling my hair out trying to add an app I
created to a Facebook fan page. Creating the app was trivial compared to
actually adding it to the page. Every help page says something different, and
the links that were supposed to be there weren't. The instructions given are to
follow the "View App Profile Page" in your app's settings page, but this link
isn't always there for whatever reason. To add your new app to a page, use the
URI below, replacing APP_ID with the ID of the app you want to add. It's on the
summary page of your app in the developers area (for now).
That will bring up a dialog allowing you to add the app to any page or profile. Courtesy of this topic on Stack Overflow.