Java: DrJava IDE

Rice University is working on a nice IDE, DrJava, that can be downloaded freely from drjava.org. Some features:

Installing DrJava

Setting the Preferences

There are several preferences that you will probably want to set using the Edit > Preferences menu item.
Miscellaneous
Resource Locations
To add external packages to the CLASSPATH, click ADD and select the directory or jar file you which to add (eg, C:\javaclasses\cs1.jar).
Display Options
Check Line Number Enumeration.