A useful tool for programmers, designers and power users alike that I came across the other day (credit goes to Mark Boulton in his booklet Five Simple Steps – A Practical Guide to Designing for the Web) is DropBox.
In their own words, “Put your files into your Dropbox on one computer, and they’ll be instantly available on any of your other computers that you’ve installed Dropbox on (Windows, Mac, and Linux too!) Because a copy of your files are stored on Dropbox’s secure servers, you can also access them from any computer or mobile device using the Dropbox website.”

It’s a simple yet immensely useful tool. Forget about emailing or IMing files around. No more FTP. Setup the dropbox on all the computers you want to share the files and they instantly sync between them, with basic version control (it’s not SVN but should be good for most casual use) and backup (via Amazon S3). It works native in your file browser, just as if it were a local folder. Changes sync in the background automatically — it works pretty quickly. The easiest way to share files that I have found to date.