My current setup, Live For Speed Rules!! The Wheel cost $5 at the second-hand store :)
Wooden Stand, cheaper, no welding.
I have full adjustment of all angles, I could even lean the screens together forward or backward without upsetting the mirror alignment.
I hold the acrylic on by setting it over these screws, one per side. I need to get some real glass, this plastic is very bad, I will need a different mounting method then.
This way I can slide the monitor in two dimensions, as well as twist it for alignment. I should be able to move up to a 19" monitor (or 22" wide) as well, although I may need to brace the arm better from the back.
Simple but effective, that won't be going anywhere soon :). If I did it again I would use fender washers. The rod actually threads into the wood, that is how tight I drilled the hole. (unnecessary, but I had the drill bit out already.)
Serendipity, I made the stand this wide to hold my keyboard for FPS games, lo and behold that my steering wheel is a perfect fit.
yes it is blurry, but you can see both screens. My top screen is dying a little, so with the direct-view on 0% brightness they still aren't even :(. But you still can see both screens are quite well aligned.
As you can see, the tops of both screens are together, seen through the mirror they both have the same viewing angle.