If you know of an open source project that seems like fun to hack on, working on that might be helpful in a couple of ways: It builds your skills in whatever toolset the project uses, and also (if you're good) can help get you potentially useful contacts. (The best matches here for your skill set might be Java open source projects. There are plenty of them, but this, unfortunately, isn't the best place to find out them.)
Alternatively, if there's some small utility you could write (something the scale of, say, a jQuery plugin), or a small Django or Rails website, it might be useful to write that, package it, and write it up. There are far worse things to show an employer these days than an interesting portfolio of stuff on github.
EDIT: this essay on finding interesting stuff to work on just showed up in the 'new' feed, and might be useful: http://svpow.wordpress.com/2011/02/03/tutorial-12-how-to-fin...