What options are there for good, cheap online backup of photos?
I am currently travelling quite a lot and sometimes carry up to two hard drives with me. While they are also heavy I don't feel completely comfortable carrying them everywhere or putting them in packages for shipment.
I'm quite a fan of using cloud based services. I'm curious if there is a cloud solution to back up pictures, preferably featuring the storage, archiving and sorting (folders and tags) of thousands of pictures in original size. In the best case as cheap as possible or for free.
The closest service I found is Google's Picasa Web Albums which offers - if you are a Google+ user - the storage of as many pictures as you like as long as their dimensions are smaller than 2048x2048 px (see here http://support.google.com/picasa/answer/1224181?hl=en). Are there others?