And just to run a single HD plus monitor (and in intensive games a full HD monitor), you need a 6950/6970 CF or GTX 570/580 SLI. So to be able to justify 3 monitors, you will need at least 7970 CF or Quad CF or so.
Because I like to have a minimum of 50-60 FPS at everything maxed out(except AA). And I want this even in games like Crysis, GTA IV, Metro 2033 etc. At the moment I can't even run Crysis or Metro 2033 at full HD, so I will definitely not even think about increasing the rez.
To play these maxed out at full HD, the minimum requirement is 6950/6970 CF which I don't have anyway.
If I had to buy a better monitor, it would be like this:
27" LED
even more money
Dell U2711
even more money
46-55" LCD TV
either of the three, but definitely not more monitors!