Download Processing (v2.2.1 verified works), open yumm.pde, and run.
Click on any of the 27 rules in the menu to the right to change the bottom output cell.
One-dimensional cellular automata are neat. The link describes the set of Elementary Cellular Automata, which have 2 states. This tool lets you explore the entire space of 3 state one-dimensional cellular automata.
The entire space! That's over 7.6 trillion possible rule combinations! Though many of them are isometric. Here are some pretty examples:
