Imgur - Imgur is a free and simple image hosting service with image editing feature. Signup is optional.
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.
Flickr - image and video hosting website
digiKam - Professional Photo Management with the Power of Open Source
Photobucket - Photobucket offers image hosting and free photo and video sharing.
imgbox - Imgbox is a free image hosting service.