Before the rabbit pistol the best ray gun in the toy store (above) was the one from the Mars Attacks movie. My hunch is that the original prototype looked a lot better than the final production model, but it's still a good effort. Mike says there was an earlier model of this that looks better than the one shown here.
I love the idea that the gun is powered by a squirrel's brain. Of course the brain requires a life support system, thus the hose.
For years the best ray guns were water pistols (above) and nerf dart launchers.
Some of them were really elaborate (above).
My guess for the near future of ray gun toys is that they'll combine the best features of the Rabbit Invasion pistol with that of the Mars Attacks pistol. The next pistols may retain the cartoon head but be guided by human brains, maybe the brains of miniature plastic humans. Maybe they'll be powered by a globe full of real flies.
Yikes! I grossed myself out!