MiMedia offers media streaming, but I can't recommend it for that purpose. In my tests, MiMedia choked when uploading videos as small as 18MB. Also, using MiMedia's Dropbox-style folder on Windows 8 caused Windows Explorer to hang repeatedly, a problem I didn't encounter with any of the other cloud services.
If you want to stream music online, a good choice is SugarSync, which offers music streaming as part of its service. You could also just stick with Google Music (not previously mentioned, as it doesn't offer traditional storage), which lets you upload 20,000 tracks from your personal music library and stream them from any online location you can reach.
For online video streaming, you can use Jolidrive (see below).
Backups and cold storage
SpiderOak and Ubuntu One let users backup specific folders to the cloud. MiMedia's desktop application also works well for folder-specific backups, which don't rely on manual uploads or file manipulation.
Box and Mega are ideal for storing files that you rarely access but want to keep in the cloud, especially if you can snag one of Box's 50GB free introductory deals. You can also use Mega's 50GB of free storage to store ample wares--but again, don't rely exclusively on Mega for file storage. It might go away.
Bringing it all together
Managing multiple cloud services can be a pain, even with widespread Windows Explorer integration. Fortunately, you don't have to handle the job on your own: Jolidrive from Jolicloud creates a cloud services dashboard that displays your Box, Dropbox, Google Drive, SkyDrive, SugarSync, and Ubuntu One files in one location. Jolidrive is especially helpful when you're on a public PC and you need access to your cloud files.
The service adds a few handy features of its own, such as music and video streaming, Google Drive document editing, and integration with Pocket and Instapaper. You can also connect various social networks--including Facebook, Google+, and Tumblr--to Jolicloud to view your social feeds in a Pinterest-style layout.
Jolicloud doesn't offer a way to transfer files between cloud services. A similar service called Otixo does provide that functionality, but Otixo no longer offers a free version of its service, alas.
And that's that. Welcome to your fully functional and uber-flexible hard drive in the cloud! Now, how to fill all that free space...
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