Mine was inspired by Slick's. http://libgdx.googlecode.com/svn/jws/particle-editor.jnlp
Building good particle effects requires a lot of experimentation. Often images combine in cool and interesting ways when moving, blending, scaling, and rotating, and it is difficult to visualize. Also a tool lets you play around with reducing the number of particles to a minimum without losing the effect.
You could use one of the tools above to design and then go off and write your own effect specific particle emitter for ultimate performance. Still, I have tried to make my general purpose emitter efficient. I have been meaning to replace the bitset junk with boolean, which I have a feeling will be faster since there are typically not many particles for a single emitter.