You can make a living writing j2ee apps for the rest of your life, but I'm not sure you'd want to... Here's a couple of things that have recently helped me broaden my programming horizons:
Learning lisp from http://gigamonkeys.com/book/. I still completely suck at lisp, but my eyes are opened to what you can do with functional programming and metaprogramming.
Picking up Ruby and learning RoR. Any dynamic language would be helpful to know... take a look at both python and ruby and learn more about whichever you like better.
I've also gotten heavily into javascript recently because of jquery. I'm pleased with how flexible the framework.
None of these things are something you can go pick up in a one week training course. They're something you have to practice day after day to get better at. The most helpful thing you can do is to get a side project with some new language/framework and get cracking. Best way to learn imo.