Try 'Dropbox' (www.dropbox.com). Its main use is sharing files between computers - once installed, there's a magic folder, and anything you put in that folder gets automatically copied and synchronised to the matching folder on every other computer you have dropbox installed on, in the background, with every version of every file archived on the dropbox server, so you can revert back to any version you want.

Inside that dropbox folder is another called 'public' - any file you put in there is accessible on the web, by anyone (from dropbox's web servers, not your PC). Right-clicking on the file on your desktop copies the URL of that file into the clipboard, and you can paste it into an LJ entry, facebook comment, etc.