Spamsweeper - try it out - A minesweeper rip-off, developed for my Introduction to Programming Languages and Data Structures. This program was my introduction to data structures.
Maze Maker - try it out - Lets you draw a maze and then automatically finds the shortest path through it using a breadth-first search algorithm. I was inspired by a class project to implement bfs for maze solving, and made it into a full applet.
Fractal Maker - try it out - Generates a few different fractals at various resolutions and with different color palettes, now with ability to zoom. I've been interested in fractals and their mathematics since high school and have always wanted to code up a fractal generating program - once I knew enough programming, this is what I wrote.
Particle System - try it out - Originally I wanted to make a fireworks applet, and this is what it evolved into. I also took the opportunity to make a command line interface class, for future use in my java applets, but since then I seem to have moved to OpenGL.