So you did not grow up with MS-DOS 3.2 like the rest of us, and when it comes to copying files you stick to the good old Windows Explorer. Well that is all well and good, however if you suddenly need to copy a LARGE number of files or some very large files this can become an issue, the error handeling capabilities of Windows Explorer just aint that great.
You may have heard about Robocopy, a cool little – rather old by now – utility from Microsoft. Robocopy stands for Robust file copy, and it has the ability to mirror directories event down to ntfs rights, very nifty (I have used it since the good NT4 days) however it’s a good old MS-DOS commandline utility so you have to write pages with switches to tweak it just for your task.
To my amazement however I just realized that Microsoft actually released a GUI for the util back in 2006 
well well, so now there is no excuse not to use it and save yourself a lot of time and pain..
http://technet.microsoft.com/en-us/magazine/cc160891.aspx
Now Robocopy is a VERY nice utility and still the most reliable I know of, however as mentioned in an earlier post Terracopy is quite a competitor, and I would be sure not to miss giving it a go too (its somewhat easier to work with).