WormHoleX makes it easy to send large files (and small files too, of course) via email or instant messenging.
When a file is dropped into WormHoleX, it uploads the file to your .Mac account (iDisk does not have to be mounted). At the same time, the link (i.e. URL) for retrieving the file is automatically copied onto the clipboard. All you need to do after you drop the file is paste the URL into your email or instant messenger and send