SyncBack (synchronize files to USB drive)
"SyncBack is our free computer backup software that helps you easily backup and synchronize your files to the same drive, a different drive or medium (CDRW, CompactFlash, etc), an FTP server, a Network drive or even a Zip archive. The best free backup software just got better!"
- freeware, home, and professional editions available - plus: configurable, stable, relatively quick, preview actions before the run - minus: changed folder names generates a copy under each name - catch this in the preview
I use it regularly to synchronize file collections between various workstations.