I am trying to do the same thing. Going to get 3 of the same 27inch korean IPS monitors and mount them in portrait mode. The problem with all the above is either:
A) They do not support 27 inch monitors
B) They are not available
Right now I cannot find anything out there that is an acceptable option. Most stands will only take monitors less than 26in.
I did find this:
http://www.ergolcd.com/Ergotech-Apex-Triple-900-F20-B03.html
http://www.ebay.com/itm/Ergotech-Group-900-F20-B03-Apex-Triple-Multi-system-/230894688245
But I really don't find it necessary for the monitor stand to be almost as valuable as the monitors themselves.
An additional complication for me is that I have a L shaped workspace so the monitors will be centered on a corner, so the edge clamp versions will not work for me. I'd rather have a freestanding version, but I will drill holes and mount on the surface if I have too.
Looking at the measurements of some of these models that are rated for LCDs <27 inch, there is just enough space on the bar to mount in portrait mode, but sometimes the bottom edge of the monitor will be nearly sitting on the desk or worse.
Due to the increasing popularity of triple displays, someone out there is using a decent stand. Can anyone share?