Java is a really cool language with a wide variety of applications. I've been playing with the language for a couple years, though I only have three significant (yet incomplete) projects to show for it.
A simple clone of the ever-popular Windows game, Minesweeper. Here's a screenshot of my progress.
An applet to simulate the property of chemical equilibrium. You select the initial quantity of reagents, the number of random trials to perform, and let 'er rip. The relative quantity of reactant produced is graphed with respect to trial number.
Here is part of my high school senior distinction project on wavelet image compression. It takes an an image and compresses it with the Haar wavelet function and reconstitutes it. Included is a comparison with a JPEG-compressed image. Take a look at it.