Do you need another graphics card to setup three monitors?
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you need a Graphic Card that supports several monitors. This days almost all new cards can handle at least 2.
Nvidia cards can use 2 monitors for a single card. If you want 3 monitors then yo will need 2 cards with SLI.
nvidia gtx 590 or newer can handle 3 monitors with only 1 card I think
Depends on brand and model. That I am aware of, no single nvidia card supports three monitors. You would need to run two cards. ATI cards have crossfire support which supports 3 monitors but that has it’s own caveats that I am not that familiar with. Also, not all ATI cards support Crossfire. Research Crossfire before you do anything. Much also depends on OS and whether all 3 monitors are the same res, etc etc etc.
I got a 24" monitor and was briefly using 2 17" monitors in portrait mode beside it. I loved it until I realized that for multiple reasons Having my nice 24" paired with my somewhat crappy 22" was a better solution. Occasionally miss having a 3rd monitor but only when I have Blender on one monitor, Photoshop on another, and I want to change what song I am listening to or want to check something on the web.
Only the Geforce GTX680 onwards support 3 monitors by default. There are however special versions of older NVIDIA GPUs that do support more than 2 monitors (but those are advertised as such). It might also be that the dual-GPU cards like the 590 support more than two monitors, I’m not sure about that.
All newer AMDs support three monitors and more (Hydravision)
If you want to use 3 monitors spread over 2 GPUs, you don’t need SLI or Crossfire or anything. It need not even be a card of the same model or even vendor, you can just plug in a cheap secondary (pci or pcie) card if need be. (Don’t expect triple-view gaming to work in this case, though)
EDIT: I’m speaking for windows here, multimonitor on linux or mac is likely a completely different story.
Ok Ill do some more researching thanks for the info guys.
I’ve been using two monitors since about 1998 - can’t live without it. Even if your app is one monitor, it’s comes in a ton of use to look up references or keep things like your instant messengers out of the way. Even helpful for video games - look up stategies in wow on second monitor while keeping an eye on the game on first.
For Blender I tend to have tutorials/wikis etc on the second monitor - or if I’m doing texturing work I’ll pull the UV editor over to the second monitor. A billion different uses. 2 (or 3) all the way.
Yup two is the best!
I vote for 2! I myself use two monitors, it is quite handy, especially if to speak about working with graphics.
Both of the monitors plug in to your Graphics card. Modern graphics cards have 2 or more screen inputs.
The drivers take care of it all and configures them pretty much automatically.
You may need to switch left screen to right manually if it’s wrong. But that’s really easy to do in screen settings. You know, left click desktop > Screen resolution (Windows) 
Using both screens feels very natural, basically, as you reach the edge of one screen with the mouse, it jumps to the other screen.
So it feels like having one big wide screen, only that windows maximise to the screen borders instead of maximising on both of them.
No special shortcuts or any other complications.
One thing that drove me away from Linux (Specifically Ubuntu) is that It was really hard to setup the screens on the Nvidia drivers in comparison to Windows “plug in, and it works, if you have the drivers installed”.
Plus, the Unity interface, at the time I tried it, didn’t work very well with multi-screen.
Only the Geforce GTX680 onwards support 3 monitors by default.
I thought connecting three screens was possible if the motherboard has an integrated graphics card. Am I wrong?