Imgur - Imgur is a free and simple image hosting service with image editing feature. Signup is optional.
Flickr - image and video hosting website
picinfinity - Picinfinity is an image retaining/proxy site.
PostImage.org - Provides free image upload and hosting integration for forums.
PicPicGO - Bring all of your favorite photos with mass amounts of storage space.
Photobucket - Photobucket offers image hosting and free photo and video sharing.