Not sure if I’ve posted this before, but just to be sure … One of my clients (a professional writer) was upset recently to have sent several megabytes of photos to a publication only to get a rather angry response. It seems that both parties there had a rather minimal grasp of the complexities of email attachments. This service makes it easy for both sender and recipient — no extra explanations required.
YouSendIt is a “remailer” service, and it’s totally free. You go to their site, upload your file to THEIR server and type a custom message. YouSendIt then sends the person you want the file to go to a simple text message with a link to the actual file that they can download via the Web.