Oracle is one of the main players in the commercial database field and most readers will probably have come across it at some point. You can download it freely for non-commercial purposes from http://www.oracle.com/technology/products/database/xe/index.html

In this section, we'll connect the server to Oracle Database 10g Express Edition using the latest JDBC driver (11g) available at http://www.oracle.com/technology/software/tech/java/sqlj_jdbc/index.html