Alright I figured it out.

Instead of trying to chain everything together into one I changed:

$posts = DB::table('posts')

to

$query = DB::table('posts')

And split the rest off:

    if (Input::get('lookingfor')) {
      $query->leftJoin('lookingfor_post','posts.id', '=', 'lookingfor_post.post_id')
      // Lookingfor filter
      ->where(function($query)
      {
        if(Input::get('lookingfor'))
        {
          $query->where('lookingfor_post.lookingfor_id', '=', Input::get('lookingfor'));
        }
      });
    }

    $posts = $query->orderBy('id', 'DESC')->paginate(10);

    return View::make('posts/index', compact('posts', 'region_options', 'rank_options', 'lookingfor_options', 'minrank', 'maxrank', 'region', 'lookingfor'));