Oracle SQL Developer is a free integrated development environment that simplifies SQL development and management of Oracle Databases.
I have been using Oracle SQL Developer since the Beta Pre-release, and while the early versions were Oracle DB only, later versions can be used with a range of other SQL databases. Oracle are primarirly making these interfaces to non-Oracle databases available to ease migration to Oracle and so they are to some degree limited. While the database management features are not available, the ability to develop SQL queries are extensive. I have used SQL Developer with MySQL databases and it is significantly easier to use than the query page in phpMyAdmin (which you still need to use for DB management).
Microsoft SQL Server 7.0, 2000, 2005, 2008 R1 and 2008 R2
Microsoft Access 97, 2000, 2002, 2003, 2007
MySQL 3.x, 4.x, 5.x
Sybase Adaptive Server 12, Sybase 15
IBM DB2 LUW 8.x, 9.x
Teradata 12, 13
Scheduled for future release
IBM DB2 ZSeries Z/OS
IBM DB2 iSeries
And of course when used with an Oracle DB the full power of the tool can be appreciated. Having used other commercial tools (such as TOAD and PL/SQL Developer), SQL Developer is very competitive – even before you consider that Oracle have made it available as a free download.
The tool no serious SQL developer should be without.