Plane of Mirrors?
Let me reflect. Ok, sorry, I had to do it.

Seriously, pay attention to what Psion said about the mirrored version of the traveller. Also, I can't recall what it says of the top of my head, but it might be worth it to look in the DMs Guide at the mirror based magic items (mirror of opposition, lifetrapping). I don't know how helpful it would be but it could give you some ideas.
Finally, here's something I got off the web and saved to my HD, it's not D&D, but I enjoyed reading it.
"According to most people, all physics books, and so-called common sense, mirrors work on the basic principle of the reflection of light. But these thoughts couldn’t be farther from the truth. You see, the image of yourself that you see in a mirror is not an image, but, rather it is yourself. Actually, to be more precise, it isn’t yourself, but instead an identical copy of you.
According to the multiverse theory, there are an infinite number of ‘universes’ like our own, but with minor differences in the history of each universe’s events. A simple glass mirror is a gateway into those other universes, a sort of temporal anomaly. You cannot enter this other universe, however, but you can see into it. What most people think is their reflection is actually their counterpart in another universe looking in a mirror at the exact same time they are.
The reasoning behind this discovery is the ‘refraction’ of light in a mirror, or reflective surface. Mirrors and all reflective glass have an unusually high gravitational density, which means a small amount can have enormous gravitational pull. A mirror or lens doesn’t refract light; it bends it through gravity, like a black hole. (Black holes have been analyzed with the Hubble telescope and it has been discovered that black holes are just planet-sized glass discs.) A black hole has much more intense temporal anomaly effect than a small mirror, so falling through one could actually put you into a different universe.
This multiverse-mirror theory explains many natural phenomena. Finding ‘your double’ isn’t sheer coincidence, it happens when a temporal anomaly sucks your counterpart into this universe with you. When someone gets sucked out of this universe, we believe that they disappear, but they really are just relocated. Also, the Bermuda Triangle is a temporal anomaly. All of those lost ships are lost in some random alternate universe wondering what the heck happened! Déjà vu is when you switch places with a counterpart, and undergo events that you have already committed in this universe! Amnesia is an alternate effect of this place swapping. Instead of remembering the events in the other universe, you forget them all, and don’t remember who you are."
If you don't find enough info, you may want to consider doing a google search for info on mirror universes, I'm sure the web will produce lots of stuff to consider.