I've recently signed up with a lesser-known cloud service called Koofr.
Every single folder and file I have is now in the cloud and also in local Windows Explorer-style folders on each of my computers - XP is supported - plus they all appear automatically in an app on my Windows Phone, where they are on the SD card (EDIT: No they're not, just checked the card, they're in the cloud.)
2 GB is free, 10 GB is €0.5 a month, 25 GB €1 a month, 100 GB €2 a month - which even I can afford. It is extremely rare for me to pay to use anything on the net, but I have 37 GB in the 100 GB plan.
It's a little confusing to use at first, it would benefit from some detailed Help files, and I did end up with some duplicated stuff initially when I uploaded everything onto it, but once I attended to that and when I got the hang of it, it is faultless.
What is more, on my 8.1 pc changes and additions to files, such as edits to a document, are synced automatically by webDAV. It amazes me, I do some work and then think I need to sync it, but when I check the cloud application I find it has already been done, without me doing anything.