netstiff (formerly known as webdiff) is a powerful Web and FTP site update
checker. It supports a variety of different methods (diff, html, size, date,
MD5 sum, regexp) and only prints the URIs of the Web pages and/or FTP sites
that changed so that its output can easily be used by other scripts
(such as wget or mail).

WWW: http://pkqs.net/~sbeyer/#netstiff