Platforms: iOS, Android, Windows 8 (all free)
If you use Microsoft services every day, chances are SkyDrive is already a part of your workflow. The new Office applications save your documents to SkyDrive's servers by default. You can store photos, videos, and more there, too. From a SkyDrive app, you can launch the Office Web Apps in a browser to work on projects away from Word, Excel, or PowerPoint on your PC. Pay $10 to add 25GB, $25 for 50GB, or $50 for 100GB per year to your free 7GB of storage. SkyDrive and Office are also a powerful combination if you use a Windows phone.