You can use Dropbox, SugarSync, Google Drive, or Ubuntu One. All of the service provide more or less 5GB space for free. Also, you also get mobile app for each service, which means every data that you sync is always available to you, wherever you go.
Currently, I have all of them setup, plus a few other services, (Wuala, Box etc), so that in total, wherever I am, I have 40GB of cloud space going along with me, all for free.