Dropbox  (File Storage)
Store all your files in Dropbox so that you can access them anywhere in the world at any time. It’s also a place to store files you want to share through links (think opt-in freebie PDFs or audios).   Email marketing providers have size limits for attachments, as does many shopping carts.  Dropbox is a great solution for this if your product
(video, audio, ebook, etc) is over the size limits.   You can add a link to the download file in dropbox via your shopping cart, or thank you page after your customer makes a purchase, or opts into one of your free email campaigns.  
https://www.dropbox.com

Amazon S3  (File Storage) 
Like Dropbox, Amazon S3 offers file storage.   This works even better than Dropbox for file delivery for paid programs, ebooks, etc that your client purchases because it pops up on their browser allowing them to view it online before downloading it.   All you have to do is upload your file, make it public and add the link to your product.  We recommend using both Dropbox (for storage of ALL your files, images, programs, etc, as it holds a large amount at a very low price), and Amazon S3 for program delivery storage only (ie the paid products you sell such as ebooks, PDF files, etc)
https://aws.amazon.com/s3/

Google Drive  (File Storage)
Accessible from anywhere, Google Drive can be used by anyone with a gmail email
address.  It’s a cloud based storage system that also allows you to host documents, edit the document in real time with someone else, and share them.
https://www.google.com/drive/