Google Drive is a free cloud based service that can be used for docs, presentations, audio and video files, and spreadsheets. All docs are compatible with the major office suite programs out there. It includes 15 GB of storage with option to upgrade to 100 GB at 1.99 a month to one 1 TB at 9.99 a month. Security is through gmail, so password strength plays a factor.
I chose this as a gmail user, and find it very convenient to use as a workstation, whether on desktop or mobile. The ability to share and allow others to edit docs makes collaborating easy, and personally the only other cloud based service I use is drop box, and I find Drive to be cleaner and a bit more intuitive from from the user point of view.