Cloud isn't a type of technology per-say, it's more of a marketing term. Online data storage will always be referred to as a "cloud" thing because marketers figure the easiest way to describe the phrase "uploading files to an external server for online storage" is "put them in the magical cloud for as long as you want!"

That said, in addition to Google Drive and Dropbox, I believe Microsoft also has a similar service, though I'm not sure how well it works or how to use it in the first place.

There's also Mediafire, though things you upload there are uploaded for public consumption. If you had some Tron artwork you wanted to keep to yourself, you would probably be safe uploading it as there are a lot of public Mediafire files that would more than likely make yours near-impossible for someone with malicious intent to stumble upon, but you wouldn't want to be putting stuff like your Social Security Number or credit card info on there.

Now, those two services I believe are free. I'm not entirely sure about the Microsoft one, but I know Mediafire is free. The amount of space the two provide is not infinite, though I've been uploading stuff to my Mediafire account on and off for years and I haven't run out of space yet.

I'm not sure about most of the other services shown on this website, but you may want to check out some of these reviews if you're willing to pay a monthly fee for online storage:

http://online-storage-service-review.toptenreviews.com/
Additionally, as a bit of a warning, be careful with how much data you're uploading and downloading to and from your online file storage service of choice. Most internet service providers have a bandwith cap, which some people can quickly exceed by doing multiple massive file transfers to and from online storage services. I read an article a while back about a person who had done so by uploading and downloading terabytes of high resolution photos and raw sound FLAC files to and from multiple online storage services. He quickly exceeded his ISP's bandwith cap and they consequently shut down his internet.

Hope this helps!

EDIT: By "Google's free service" I'm assuming you meant Google Drive? It can work with folders, but only in the Google Chrome browser, which is silly. A workaround would be to right-click the folder you want to upload, go to "Send to", and then click "Compressed Zip Archive" (this will be different if you're on a Mac, but there is a way), and then upload the resulting .zip file. That's what I do.