A spun-off product formerly integrated with Google+, Google Photos is a photo backup and viewer service by Google that comes with build in photo editor interface.
A photo backup service and viewer by Microsoft
Mega is a cloud service founded by Kim Dotcom.
Shoebox is a photo backup and viewer service with free unlimited backups that also has paid options.
Copy.com is a cloud storage service by Barracuda Networks that comes with it's own photo backup service called "Photocopy".
iCloud is a cloud storage by Apple Inc. that can allows users to synchronize their photos, data and files between apple devices and PC.