Over the last month or so I've needed to send and receive a lot of large files (Final Cut project files, songs in AIFF format, DVD burn files, and so on). By "large" I mean in the 20mb - 4gb range. These files are usually too large to be sent via email because of file size limits, using an FTP site can be a hassle (as David Pogue has noted), and sending files via DVD-Rom via mail or FedEx is (comparatively) slow and pricey. For me, the solution has been to share these large files via a few of the several services that exist online. I have used YouSendIt, FileFactory, and Pando. All have worked just fine.
The first two are file-hosting sites; Pando, on the other hand, is a stand-alone application. It requires a (free) download, but it also allows for the sharing of much larger files.
If you find yourself needing to share large files and don't know where to start, a fairly comprehensive listing of file hosting sites is available on Wikipedia. You can also check out this article, which surveys some of the main services.