I use Java and jcreator in my classroom. Both free. There are also free tools that help students get a grasp of concepts before mastering the syntax (bluej, scratch, alice)

There are also packages that help with teaching, karel J robot comes to mind.

I also use codehs.com as a supplement for my class.

Great, thanks. Any thoughts on what works and what doesn't, more generally?

Also, what do you teach and to students of what levels of aptitude and skill?