I have Dropbox, which I use a lot because my team uses it. And I use Google Drive as we are a Google Apps based company. And I use ownCloud because I can do whatever I want there, there is no cost really, as I already have the colocated server. They all have their strengths.

There are also very cool solutions such as routers that allow you to have a hard drive on them that can be accessed from anywhere, and bittorrent sync.

You should look at bittorrent sync as it is free and may do everything you need, and you can run it on your existing computer(s).