Treecomp - TreeComp is a utility to keep 2 directory trees and the files within the directories in sync. Download from this site!
Truck - A faster alternative to FTP
rsync - rsync is a file transfer program for Unix systems. rsync uses the "rsync algorithm" which provides a very fast method for bringing remote files into sync.
CopyQueue - CopyQueue - Copying under control.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
Synchromat - Synchromat is file and folder synchronization software for Windows.