Mac: CloudApp is one of the most beautiful and simplistic applications. Not only does it look great, it’s easily one of the apps I use the most.
Once you downloaded and installed CloudApp from the Apple Store, it puts up a little cloud icon on your status bar. When you drag ‘n drop a picture/ file on the cloud, it’ll upload that picture/file and copy the url to your clipboard.
Furthermore, there are a lot of shortcuts which you can use to make uploading and sharing even faster. Per standard it’ll automatically upload screenshots to the cloud.
Best of all: it’s free! So check it out!