Flickr - image and video hosting website
ACDSee - ACDSee is an image viewer that uses very little system resources, and it has a small, sleek size that won't take up much space on your system.
Imgur - Imgur is a free and simple image hosting service with image editing feature. Signup is optional.
digiKam - Professional Photo Management with the Power of Open Source
ImageShack - Unlimited space to host images, easy to use image uploader, albums, photo hosting, sharing, dynamic image resizing on web and mobile.
Dropbox - Online Sync and File Sharing