Years ago, when lava lamps were all the rage, we had a red one. Then we dropped it on the stairs and that was that. I don't know if you can even get them any more but you can make your own.
In a large vase put a couple of inches of colored water. Pour vegetable oil up until about an inch from the top. Plop a couple broken Alka Seltzer tablets (the more pieces the better) in the vase and watch your lava lamp come to life.
For the real lava lamp experience, turn out the lights and shine a flash light up from the bottom of the vase. This is good for about three minutes of excitement but, it does work over and over. Pretty cool.