Eclipse SQL Client for database querying/browsing any JDBC compliant database. It supports plugins with specialized functionality for individual databases (Oracle, DB2, MySQL, PostgreSQL, Sybase, Informix) and can be extended.
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