Platforms: iOS (free), Android (free), Windows 8
If you just need to keep personal and professional documents at your fingertips, Dropbox eliminates the need for a filing cabinet. It doesn’t come with extra services (such as the Office Web Apps, the Google Docs suite, or Evernote's note-taking features), but it’s dead-simple for uploading and syncing up to 2GB of files across multiple devices for free. Share files and folders with other users, and if you let it sync files and videos automatically from your tablet, you get an extra 3GB. Up that to 100GB for $9.99/month, or check out Dropbox for Teams, starting at $795 for 5 users, offering 1TB per person.