I find myself using Amazon S3 for storage more and more these days. Yes I have a Dropbox account, and a Box account (and probably a Copy account too). There are times that I need a little more space then I have available in Dropbox and among other things I have been using Amazon S3 to give my self a little extra space as needed.
What is Amazon S3 you ask this is a quick explanation
Here are some tools I have found useful working with my files in S3
Android: S3Anywhere Free and Pro versions available
Windows: Cloudberry Explorer for Amazon S3 Free and Pro versions available so far I have been using the free one and it is meeting my needs
iOS: AirFile Free and Pro versions available. This one is interesting as it allows me to move files from S3 to Dropbox or the other way right from my iPad (it supports other Cloud storage services as well)
Are you using Amazon S3? If you have any good tools leave a comment.