Here, in no particular order, are some of the best free solutions:
SkyDrive
If your office is driven by Microsoft software, then this is the solution for you. Totally free, SkyDrive acts like a stripped down version of Office 365. You get 7 GB of free cloud storage but you also get a whole lot more. Specifically, you get a basic online version on Microsoft Word, Excel, PowerPoint and OneNote. This means that you can, for instance, create a Word document on your computer, upload it to your SkyDrive account, and you can make minor adjustments in the cloud before downloading again. Alternatively you can create entire documents in the cloud (albeit with more limited functionalities on offer).
It is well integrated with Windows solutions like Windows 8 and Office 2013, and if you go mobile, it is available cross-platform (download Android and iOS apps for your mobile device). You can sync a folder on your PC so that whatever you create syncs with SkyDrive and it offers third-party apps (but they are not as varied as another great online storage solution, Google Drive). You could run a small business from everything that SkyDrive provides, and if you need more storage space, 50 GB, 100 GB options are available, maxing out at 200 GB at an annual fee $105.
Google Drive
Google Drive offers a whopping 15GB free and like SkyDrive, it is big on integration. Google Drive's app options (Google Docs, Spreadsheets, Presentations, and Drawing) that mimic Microsoft software options, but obviously not a successfully as SkyDrive. You can upload documents you have created in Microsoft Word and migrate to Google Drive's native format. Still, large corporations use this capability to run their offices, and so can you!
Google Drive is very strong on collaboration - two or more people can create the same document online at the same time. This is really impressive and has a number of implications for dealing with customers, especially when gathering customer requirements. Obviously, it is finitely integrated with Gmail (and Google Apps for those of you who still have free Google Apps accounts) and other services like Google+, and the 15 GB of space is growing steadily - for instance people with certain mobile phones you get 25 GB of free space. Obviously, this is a mobile option and there is a fantastic app available for Android and iOS devices. A truly great online / cloud storage service with masses of bells and whistles provided by third-party apps. Additional storage options available up to 200 GB at only $9.99 per month.
Dropbox
Dropbox is the original, and although it offers only 2 GBs of free disk space, this is a great option. It is a popular solution with a solid following that has a 'first-is-best'-type loyalty. Again, a cross-platform solution which supports desktop and mobile devices, Dropbox excels in community support and a mass of third-party options that leverage Dropbox's open API format. Again, as with other options, you can sync your desktop with Dropbox so you can be sure of a cloud-based backup of anything you create. Additional storage is available up to a massive 500 GB at $499.00 paid monthly and with a 17% discount for annual payments.
Box
Box.com offers a range of features and is very much a professional's solution. Its focus is on people who need to use a range of computers to do their work and it has great backup functionality. It offers a range of options and like other solutions, provides automatic syncing with PCs and other gadgets. It also generates links for file sharing so that you can give access to documents to people you are collaborating with. It has become a popular solution with those in business and a number of well-known companies utilize its services. Like Google Drive, Box coverts large email attachments into stored files before an email is sent. User-friendly and solid, Box offers 10GB of free storage with a maximum file upload size of 250 MB. Additional storage goes up to "Enterprise" level which offers 'unlimited' storage for $35 per user per month.
iCloud
iCloud is great for people who own Apple devices (iPhone, iPad, etc.) and it's a solid option even if you don't. It syncs files on your Apple device (music, photos, apps, calendars, documents, etc.) and allows you to share saved files with whomever you please. It offers 5 GB of free cloud storage and iWork apps (particularly Pages, Numbers, and Keynote) provide a similar option to Google Drive - users can create documents like they do on their desktop using Microsoft software. Additional, storage goes up in increments up to 50 GB offered at $100 per year. This is though very much an 'Apple' solution - if your company uses Apple devices, it's a good option, if not, it's possibly not the natural solution.
Norton Zone
As Norton Antivirus is recognized as being the best antivirus solution available, Norton Zone offers a very safe place for your files. A cross-platform solution (Windows, Mac, iOS, and Android, etc.), it excels at providing security options. A downloadable app sits on your PC and anything you put in this 'folder' gets sent up to the cloud, meaning efficient syncing alongside peace of mind. 5GB is available free of charge while personal plans go up to 100 GB at $11.99 a month or $119.99 per year. Business users get unlimited storage for $75 a user per month or $720 per user per year. Norton Zone offers built-in device management including 'Mobile Password Management' so users can block access to lost devices and wipe their data remotely. Impressive. If security is your angle, this might be the one for you.