I can’t count the number of times iSQL Viewer has come to my aid at work; it’s such a handy tool. It’s written in Java and “implements … features of the JDBC API”. I’ve used it with MySQL, Oracle 9i/10g/Express, IBM’s DB2, and Microsoft SQL Server 2005, and it works great. One of my favorite features is the ability to bookmark SQL queries for later use. iSQL Viewer is available for Windows, Mac OS X, and Linux, so try it out!