On the same topic, I'd like to reccomend a book called "Hyperspace: A Scientific Odyssey Through Parallel Universes, Time Warps and the Tenth Dimension" by Michio Kaku. It sounds similar to the one Dave reccomended, and it is quite good. It covers a lot of subjects, everything from worm holes to superstring to how to build your own time machine. It's all written for someone who doesn't have a background in physics or math (and indeed the book has no math in it), and should be fairly easy to grasp and understand. I really enjoyed it.

I'll have to check out The Fourth Dimension. By the way, Hyperspace also uses Flatland a lot. Why isn't that book BAMmed? Or is it, and I'm just a moron that hasn't seen it?