Windows: ClipUpload is about as easy as copy and click, letting you copy a file to the clipboard and clicking its icon in the task bar to upload it.
While ClipUpload is a pretty simple application, there's a slight bit of setup involved. It'll default to using imgur.com and sendspace.com to handle your uploads, but if you'd like to enter your own FTP server, you're able to do that as well. Once you have all your information supplied and ready, just copy a file in Windows Explorer and click the ClipUpload icon in the tray. Once the file has been uploaded, its URL will be added to the clipboard.
ClipUpload requires the .NET 4.0 framework to run, but other than that it's pretty much just launch and go.