Since no one mentioned it, I'd say Eclipse.
It's very nice. First and foremost, its free, refactoring works nicely, sintax highlighting is great, autocomplete is great, seamless integration with Javadocs (online or otherwise), everything is very customizable, you can put everything everywhere you want, there are plugins available for everything you can think of (and for many programming languages!), Eclipse Foundation projects are big and widespread, etc.
The whole Java stack is pretty nice to work with (Java, Eclipse, Netbeans, Javadoc, the JDK, VisualVM, the JVM, JVM based languages like Scala, Groovy, etc), even if the language itself has some rough corners that need to be fixed here and there.
LWJGL. This is self explained, no OpenGL in Java if there are no wrappers for the C bindings Besides, it includes functionality found on various libraries like freeGLUT and GLEW, and it is updated very fast once a new OGL spec is released.
And gamedev.net of course!
EDIT: Forgot about FL Studio. I'm no musician though, but free lifetime updates is nice, interface is easy to use, Image Line VSTs are nice too, the only drawbacks I found its that its based on Delphi. Which means that its progress through "new" technologies (say, x64_86 support, multi platform support, etc) is as fast as Embarcadero's (that means, slow, very slow).
Edited by TheChubu, 06 June 2013 - 09:46 PM.