The Muscular Dystrophy Campaign in the UK is sponsoring a “Young Pavement Artists” competition. On their website, if you click on “click here to draw online for fun” you can use virtual chalk to draw on a virtual pavement. You can then email the link to a friend, and post the link on a student/teacher blog or website.
At our school we sometimes have poetry writing contests with chalk on the pavement. I can certainly see using this online resource as a supplement to such an event. And it can just be a simple drawing tool that English Language Learners would then describe.
No registration is required.