If you quickly and easily want to transfer something from one computer to another, you'd be hard pressed to find something simpler. iSendr doesn't require any uploading of a file to a distant server, just a peer-to-peer transfer from one place to another. The connection is one-time-use only.
It requires that the machine sending the file is online and available so this is primarily for "live" transfers. I haven't tested it on larger files.