Custom Blocks
Java is next on my list of languages to learn, mostly because I want to do some Android developing. I would recommend PHP, though. One, it's free compared to ColdFusion and Microsoft's Asp, and two, Facebook and MediaWiki are written in it. And Web scripting is useful™.
I don't have a Facebook(yet, people keep yelling at me to get one). Java's syntax is similer to C, and I'm buying an android phone is about a week(so I can write stuff on it) We could experiment together. But yes, web scripting is very useful.
If you're interested in Java and webapps both, JSP might be up your street. It has died a death fairly badly in commercial terms, but there's nothing stopping you grabbing Tomcat and playing with it. You'll probably learn better habits than PHP will teach you.
I can also strongly recommend getting good at embedded programming, though in most cases you'll be using a high level language like C/C++. Being able to write for memory constrained devices is a skill that's very much in demand, and sadly rare. If you want more serious playtime, I can heartily recommend buying a Chumby One. It's cheap, fun and is documented and hackable right down to the bare bones. It runs one of these and has nice handy pads for attaching an RS232 port to.