If you use cloud storage such as Amazon S3 and if you’re a Windows user, you may want to check out Gladinet, a tool which I regularly use and recommend. Basically Gladinet creates a virtual drive on your computer. Then, through the Gladinet Cloud Desktop Management Console you can mount cloud storage as folders on this drive. I use it almost exclusively for Amazon S3, but it supports Google Storage for Developers, Windows Azure, Windows Live Skydrive, box, custom FTP servers and many more. What I like about Gladinet is that you only need one software to access all of those providers and that it really works like a local drive (it has its own drive letter) from all applications, even from command line, unlike network paths or Windows Explorer extensions.
The basic version is free. There are premium versions with remote backup and other features.
What I would really like to see however is improved Picasa support (currently I can only access thumbnail-size pictures), support for Dropbox (because I’m looking for a good way to access files in Dropbox without syncing to my desktop) and also support for SSH File Transfer so I can get rid of WinSCP. Hopefully someone will read this and write a plugin :-)