Google Drive is an excellent cloud storage and file synchonization service, and comes with a generous 15GB of free space. While Google Drive also has a paid 1TB tier for the same $9.99 per month as Dropbox's 1TB tier, there's also a 100GB tier for $1.99 a month, if you need just a bit more space.
If you use the Google Office apps with Google Chrome, they're saved to your Google Drive automatically and can be shared from there. You can selectively allow other people to access certain folders and files, which makes it great to share with family or colleagues.
If you have a Chromebook, you already have Google Drive. For PC and Mac, there's the Google Drive client which will sit in your task bar or dock. For mobile platforms, there's an app in your App Store. You can't install Google Drive on a Kindle Fire -- Amazon has made it incompatible -- but you can use the ES3 File Explorer (more about this soon) to access your Google Drive. Your login is your Google account (probably your gmail login), and once they're synced, you'll be able to save and retrieve your files from any device you have.