I prefer using Sun's SunOne IDE. It seems to work
fairly well, and it's free.

There's also NetBeans (http://www.netbeans.org) which is free and JBuilder
Personal Editional (http://www.borland.com/jbuilder)

My previous company 'recommended' that we all adopt NetBeans as our IDE.

I was under the impression that Sun One was Netbeans.

I believe that SunOne Studio is based on the NetBeans framework -- which is
open-source. My impression is that Sun takes NetBeans, maybe makes a few
tweaks to the IDE and then releases it under the name SunOne Studio.

I know JBuilder is more robust and more easy to
use than SunOne Studio. But it does not like the idea
you switch into different JDK version unless you
willing to pay. Is NetBeans following the same
approach?

I use Forte for java  Community Edition, which is based on NetBeans.
I believe that Forte is the predecessor of SUN ONE Studio.

In Forte you can change the "javac" to another "javac" in the Project
properties. for example, if I have a project compiled in JDK 1.4, I
can change the java compiler to the JDK 1.1.8 compiler by setting the
javac options to "C:\jdk1.1.8\bin\javac" (or where ever your JDK
1.1.8 compiler is located). Then when I build my project, it will use
the JDK 1.1.8 compiler instead of the JDK 1.4 compiler.

SUN ONE Studio community edition is free (I think) for downloading.

If you are evaluating Java IDE, you might want to consider Metrowerks
CodeWarrior. CodeWarrior for Windows makes it even easier to switch
java compiler versions.