In a direct response to RW's January blog entry, Oracle released a new GUI development tool, SQL Developer (it used to be called Project Raptor), in March.  With SQL Developer, you can browse and modify database objects, run SQL statements and SQL scripts, and edit and debug PL/SQL statements (it uses an enhanced version of  SQL Worksheet that includes an Explain Plan window, and various output windows ). You can  run any number of provided reports, or create your own. The tool also has a very good help interface, a snippets feature for inserting code fragments, and a data import/export function.   Since SQL Developer leverages the JDeveloper IDE,  you have the option of writing extensions. The tool also has a very good help interface and a snippets feature for inserting code fragments.   

While it not be as loaded as some of the commercial tools like Toad, it's FREE (download it at otn.oracle.com) and since it's written in Java, it's multi-platform.  

I installed a copy and it's a nice tool for developers.  The screen refresh can be a little buggy, but there are some parameters you can set to tweak that.