With PR#249 the AsseticBundle (by default included in every symfony-standard-based Symfony2 application) supports the cache busting worker out of the box.

assetic:
    workers:
        cache_busting:
            enabled: true

What happens: It will create different file names for different file contents, not only on the file name (At least it should, I haden’t time to try it yet). This is cool, because now you don’t have to take care about cache invalidation for assetics assets yourself.