Mirroring

HTTrack Website Copier
Customizeable web site mirroring tool for Windows and Linux/BSD. [GNU GPL]
http://www.httrack.com/

Rdist
A program to maintain identical copies of files over multiple hosts.
http://www.magnicomp.com/rdist/rdist.shtml

Rsync
Secure remote file transfer.
http://samba.anu.edu.au/rsync/

SiteUpload
A small .NET command-line utility that uploads whole directories to a FTP server. Smart enough to upload only changed files.
http://www.jelovic.com/siteupload

Teleport Pro
Professional website download tool including a GUI and graphical feedback of download progress. Can also understand websites with complex dynamic HTML and Javascript, and be used for offline browsing.
http://www.tenmax.com/teleport/pro/home.htm

WebGet
Downloads files specified in a URL list, which can be in plain text or GetRight format. Designed to be used together with WebSuck (available from the same site) which can extract URLs from web pages.
http://www.ake.nu/software/webget/

WebLech URL Spider
A web site download tool in Java, which supports many features required to download websites and emulate standard web-browser behaviour.
http://weblech.sourceforge.net/