Rhino,

SchemaCrawler is written in Java, and is a command line tool, with an
ant task too. It can dump your database schema (metadata), as well as
data into a text file (plain text, CSV or XHTML). All of these text
file formats are designed to be diff-ed. (You will need to use your
favorite diff tool to do the diffs.) It is platform (database and OS)
independent.

SchemaCrawler is open source, and hosted on SourceForge.
http://sourceforge.net/projects/schemacrawler/

Sualeh.