There are plenty of file sharing, or file storing, services out there that store information in the cloud to be accessed anywhere. Box is doing it for enterprise. Apple is doing it with iCloud. Microsoft is doing it with Azure. Google is doing it with Drive. But beyond all of these, Dropbox has always been my go-to client for online storage.
Due to competition from other services in 2014 (namely Google Drive and iCloud), Dropbox has been forced to drop the price of its subscription service (called Dropbox Pro) and increase the storage. For £7.99 a month, users get 1TB of space, accessible from any device (for comparison, Google charges $9.99/month for 1TB while Apple charges £14.99/month for the same) with the free tier offering 2GB of space, upgradeable through promotion to friends.
Dropbox creates a simple folder on your computer which can be accessed from any device, alongside a web based interface. As such Dropbox is not tied to a major corporation and so can work freely between any software or hardware; there is no necessity to use Google Docs or Apple's iWork and no bias towards a certain device, both of which ruin the experience of Drive and iCloud somewhat.
While there is always the (faint) possibility that Dropbox will fold, the company has grown at a pace during 2014, introducing new, and better, apps for all major platforms. Investing in a Dropbox account has never been more attractive.