SQuirreL SQL Client is a graphical SQL client written in Java that will allow you to view the structure of a JDBC compliant database, browse the data in tables, issue SQL commands etc.
Quantum is a database plugin for Eclipse (needs GEF, Point Eclipse at http://quantum.sourceforge.net/update-site). It currently supports most databases with a JDBC driver. It shows tables, views, and sequences in a tree format and provides an SQL editor
DBPad is a GUI-based SQL client for relational databases. As long as you have a JDBC driver for your DB, you can use DBPad to view or manipulate your data and metadata of your tables.
JSQL Edit is a database-independent SQL client that allows graphical manipulation for making queries to databases. JSQL Edit is written in Java and uses JDBC for connectivity and Java Swing for a graphical user interface.
ViennaSQL is a GUI SQL client written in 100% Java. ViennaSQL can communicate with any database that has a JDBC driver. It should run anywhere Java runs.