Ergotron makes some nice stands. I believe you can do a 3x3 with up to 22" monitors.
However, test this first. (Use shelves, etc.) You are just going to strain your neck, IMO. I tried a 2x2 and had to go to 4x1. It's actual 2 x 1x2, since you cannot put 4 22" monitors on a single cross-arm.
They are very good about walking you through configuring a custom setup if you call them by phone. The best prices you can find are on standard configuration (1x2, 2x2) but you can still find discounters who will sell you parts. Best thing is to see if you can go with a standard configuration and then add parts.
I decided at one point I wanted to switch from weighted desk stands to a wall-mount. Unfortunately, the wall mount is an entire different mounting system. I couldn't use the existing poles.
So, here is a little trick: I went to Radio Shack and spent something like $12 total on two TV antenna wall-mounts. Mounted these to the wall, and mounted the poles in the antenna mounts.
It's pretty cool, as all my wires are hidden behind the monitors, which just float off the wall. Next comes the gutsy move of an all-plexiglass desk. (Got the plexi base, need to have the top made.) My keyboard and mouse are already on a Herman Miller Scooter. The computers are in a rack-cabinet to the side. There's a wiring channel on the wall behind the monitors which is not visible. I know, plexi scratches. But you can take the scratchs out. Not so for glass.
Now, imagine the average programmer or webmaster trying to have a plexiglass desk with NO wires showing! But I should be able to pull it off. The reason for this is that the desk will cover the fixed half of a sliding glass door, looking out on San Diego Bay. Don't want to block the precious view. :)