There are many cloud-storage solutions out there, but Box is my favourite.
My app-session #3: Box
Anything in my “Box Sync” folder on my MacBook also goes into the cloud on Box.com. When I am teaching, and need to send a PDF to a student, I pick up my iPhone or iPad and open the box app, find the file I want to send, swipe across it and choose “link”, and then email the link to the student, all from within the app. This also means you do not need to send the actual file via email, which would take longer (especially if it’s an mp3 or any large file) – you just send the link – then the recipient can download it whenever they want.
I keep my tuition material, tuition MP3s backups of photos, and a good number of website-related documents and PDFs in Box and it works really well.
The apps on iOS are fantastic too. Get a free account at box.com