you can make plasma by lighting a match, blowing it out, then putting it in the microwave. After a few seconds (sometimes as much as 30-60), balls of plasma form and start bouncing up on the ceiling of the microwave.
Edit: Oh yeah, you have to actually turn the microwave on once the blown-out matches are in it. It's also a good idea to put the matches on something that you don't really care about (old glass plate, etc.)