I'm a huge fan of Robocopy, a command-line directory replication command originally available with the Windows Resource Kit, and more recently with Vista and Windows Server 2008. Unlike Copy and XCopy, Robocopy implements reliable copy or mirroring of entire folders of any size.
During the copying process, it ensures that all NTFS ACLS, attributes, owner information, alternate data streams, auditing information, timestamps and properties are copied. Even security information will copy if you explicitly request it using the /COPYALL switch. Additionally if there's a disruption or outage during the process, there's a resume copying feature that works locally and over network connections.
That said, recently I've been using the new Richcopy which is basically RoboCopy with a nice Windows interface on it. If you're not a fan of the command line, or would just rather use something more visual, then you might want to try out Richcopy. It can copy files from multiple locations or folders into one location, as well as copy multiple files in parallel since it has multi-threaded support.
Robocopy - Command-line
Richcopy - GUI