I've been using and recommending SyncToy 2.0 Beta for a while now, but I just noticed it went final a few weeks back:
Brief Description
SyncToy helps you copy, move, rename, and delete files between folders and computers quickly and easily.
Overview
SyncToy 2.0 for Windows is available as a free download from the Microsoft Download Center. The easy to use, customizable application helps you copy, move, rename, and delete files between folders and computers.
There are files from all kinds of sources that we want to store and manage. Files are created by our digital cameras, e-mail, cell phones, portable media players, camcorders, PDAs, and laptops. Increasingly, computer users are using different folders, drives, and even different computers (such as a laptop and a desktop) to store, manage, retrieve and view files. Yet managing hundreds or thousands of files is still largely a manual operation. In some cases it is necessary to regularly get copies of files from another location to add to primary location; in other cases there is a need to keep two storage locations exactly in sync. Some users manage files manually, dragging and dropping from one place to another and keeping track of whether the locations are synchronized in their heads. Other users may use two or more applications to provide this functionality.
Now there is an easier way. SyncToy, a free PowerToy for Microsoft Windows, is an easy to use, highly customizable program that helps users to do the heavy lifting involved with the copying, moving, and synchronization of different directories. Most common operations can be performed with just a few clicks of the mouse, and additional customization is available without additional complexity. SyncToy can manage multiple sets of folders at the same time; it can combine files from two folders in one case, and mimic renames and deletes in another case. Unlike other applications, SyncToy actually keeps track of renames to files and will make sure those changes get carried over to the synchronized folder.
SyncToy 2.0 adds a huge number of new features. Check out the Web site linked above for details. This tool is awesome.