Evil Mad Scientist is always full of surprises. If you have the time, you should really browse their archives, its is just chock full of interesting work and DIY projects. Perfect for Halloween is this post from a few years ago where they take run of the mill Lego minifig and turn it into the perfect Halloween toy by adding LEDs for that creepy glowing eye effect.
While fun for Halloween, I believe this would also work well with any Sci-Fi Lego setups you might have in mind.
How to hack LEDs into Lego minifigures for Halloween [@] Evil Mad Scientist