global variable for all controller and views

At first, a config file is appropriate for this kind of things but you may also use another approach, which is as given below (Laravel - 4):

// You can keep this in your filters.php file
App::before(function($request) {
    App::singleton('site_settings', function(){
        return Setting::all();
    });

    // If you use this line of code then it'll be available in any view
    // as $site_settings but you may also use app('site_settings') as well
    View::share('site_settings', app('site_settings'));
});

To get the same data in any controller you may use:

$site_settings = app('site_settings');

There are many ways, just use one or another, which one you prefer but I'm using the Container.

Okay, I'm going to completely ignore the ridiculous amount of over engineering and assumptions that the other answers are rife with, and go with the simple option.

If you're okay for there to be a single database call during each request, then the method is simple, alarmingly so:

class BaseController extends \Controller
{

    protected $site_settings;

    public function __construct() 
    {
        // Fetch the Site Settings object
        $this->site_settings = Setting::all();
        View::share('site_settings', $this->site_settings);
    }

}

Now providing that all of your controllers extend this BaseController, they can just do $this->site_settings.

If you wish to limit the amount of queries across multiple requests, you could use a caching solution as previously provided, but based on your question, the simple answer is a class property.