Dropbox, a very popular file sharing service, cross-platform including web-based. I like it. Installed in Linux and Android device. If you don’t know this, you should register one and use it. Store some of your useful data to the cloud. In order to avoid the security hole like this, I didn’t put any important data to the cloud.
Another similar service is Ubuntu One. I registered it when I was using Ubuntu. But after I changed to Arch Linux, Ubuntu One wasn’t listed in the official repository. That is why I use Dropbox. But today, I just found that now it is in the official repository. Sign in with my previous account, everything works fine. Yeah, Ubuntu One also support mobile device and Windows. How great it is.
Another service I am considering is Google Drive. There is a related project, Grive. However, it requires manual synchronise.