I discovered some days ago a secret Symfony 2’s helper. I call it secret because I can’t find it anywhere on the documentation.
Edit: Here it is on the Symfony2 book: Embedding Controllers

{% render %} is used to show an action’s response in a Twig template. It’s very useful when wanting to show a dynamic content in all the app’s pages.

Example: Displaying online users’ counter

Create a onlineUsersAction() function

That function fetches, processes the result and returns the counter of the online users.

Create a Twig template that displays the response returned by the action

The syntax is the following:

  {% render "LiveGeekBundle:Default:onlineUsers" %}

Knowing that onlineUsersAction() is an action of DefaultController which is a controller from the Live\GeekBundle bundle.

Include that template in our application’s default layout

Thus display the online users’ counter in all the app’s pages.

Passing arguments:

You can pass arguments to the action this way:

In the Twig template:

{% render "LiveGeekBundle:Default:onlineUsers" with { 'arg1' : 'value1', 'arg2' : 'value2' } %}

In the controller:

helloAction($arg1, $arg2)

The arguments’ order doesn’t matter.

Enjoy. ;)