I'm probably one of the few bloggers here who hasn't shelled out for a .Mac subscription (and an iDisk) -- I've just never personally come across a situation where I needed one. For transferring big files I usually either throw it on a DVD or an FTP site, or I use YouSendIt for free -- there's a 100mb limit, but in all of my file transferring, I've never had reason to break it (most of what I send is audio tracks for podcasts).
And now they've released the application version of their interface -- YouSendIt Express is now available for the Mac. Unfortunately, it seems like the standalone app doesn't have some options that the web interface does (specifically checking delivery confirmation and a download limit), but for just shuffling a file off to someone else fast, it does the trick.
From everything I can find on the website, it works just great with the free account version of YouSendIt, so if you find yourself shipping off files quickly enough that you need a dedicated app to do it, there you are.