Can't get my third monitor to work

Again I'd suggest Monoprice. They are a great source for cables and adapters of just about any sort you can imagine. You could get a mini-HDMI to HDMI adapter or even a whole new cable where one end is Mini-HDMI and the other is regular HDMI. Of course the card will likely come with a Mini-HDMI adapter of some sort.

Right now running more than 2 monitors at a time is pretty uncommon so you unfortunately get to be something of a trail blazer and work out the problems yourself. The more people there are like you out there the more companies will start making cards that support 3+ monitors natively.

Just make sure that the card you get actually has three RAMDACs. It's not enough for it to simply have say 2xDVI and 1xMini-HDMI port, because odds are that HDMI port is dual-linked with one of the DVI ports, so if you use one you disable the other. On some cards you can disable the dual-link, but you're still lacking that third RAMDAC so the best you could do is two independent monitors with the second monitor mirrored on the third. The 630 you linked to (and I'd personally avoid TigerDirect, they're well known to be on the shady side) looks like it'll support only 2 monitors. If you really dig into the specifics, the 2xdual-linked DVI ports they mention will likely turn out to be that you can dual-link either DVI port with the HDMI port. On most cards there's one specific port like that because you need to share some of the internal circuitry. If a single video card supports 3+ monitors, they will advertise the crap out of that fact everywhere you look. It'll be in huge letters on the box art and they'll probably spend half the space on the back side with a blurb about supporting 3+ monitors, and they'll do what they can to draw attention to it on the specifications spine as well. They will shout it from every rooftop there is and the card will likely cost a lot more than $70.

I love monoprice, I usually buy a whole bunch of cables at the same time to save money with shipping. For this I just bought an HDMI to mini HDMI cable off Amazon ($7 on prime, not too bad for the convenience)...

I actually went to the local TigerDirect store to get this stuff (just to save time), and picked up a GT 640 there (no mini HDMI adapter unfortunately). I read all the fine print and it SEEMS to me like it's supposed to support three independent monitors, just that one being DVI-I would come out no different than as if it were VGA if it's not dual-linked. Therefore, one on DVI-D, one on mini- HDMI, and one on DVI-I. It even says "supports 3 concurrent monitors" across the top of the back of the packaging, also that it does nVidia Surround or whatever nonsense they try to push...

Here's what I got: http://www.newegg.com/Product/Product.aspx?Item=N82E16814130795&cm_re=gt_640-_-14-130-795-_-Product
--- Doesn't say in the specs how many RAMDACs there are... Is the assumption that there's only one in this case?

In the event that I get my mini HDMI cable tomorrow and it doesn't work, would this one?:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487027

If what you're telling me is the same with the 640 I'm gonna be even more frustrated haha. I can understand that they push all this different BS for gaming purposes, but what I don't get is why they don't make it obvious enough what the capabilities and limitations of the products are... This has become such a headache that if I didn't have so much vested in having built this PC (and I had the money) I'd just buy a Mac Pro and never look back.

It does appear like that one can run 3 monitors all on its own, but I guess we'll see once you actually hook everything up. At least one person in the NewEgg Q&A says that they had 3 displays set up with it, so that's hopeful though still should be taken with a grain of salt.

The 750 you linked to looks like it's more of a standard 2 display unit. The 640 specifically says something about running more than 2 monitors (which is now essentially an assumed feature) while the 750 does not.

Hope everything goes well for you. Maybe some day when I have the room for it, not to mention the money, I'll outfit myself with 4x30" 4K monitors and I'll ask you for some advice on getting it hooked up.

One other thing, is if gaming isn't a consideration, check to see if Matrox is still in business and still selling specialty video cards. They were selling dual and quad-display cards back before 3D video cards were mainstream. Just not sure if they have managed to stay in business or if nVidia or ATI (before being swallowed by AMD) swallowed Matrox. Their cards were always horrible for gaming, but for office type uses, they were just fine.

And with the new trashcan design of the Mac Pro, I'm not sure you could do much in the way of adding a second video card. Someone should create a "skin" for it to make it look like the old Mac OS trash can icon as a gag. Besides, Apple is slowly backing away from it's computer business. Ever notice how the iMac is becoming more and more like a giant iPad with its own stand or the MacBook Pro and MacBook Air hardware keep getting closer and closer to convergence, which is getting to be more and more like a tablet with a keyboard bolted on? Wouldn't surprise me if the iPad Mini just gains cellular capabilities in an iteration or two and becomes the new iPhone phablet. At this point Apple's basically out of ideas and they're left to copying what everyone's doing in the Android space and then in a stunning example of "do as a I say, not as I do" turns around and sues everyone for copying them. You'll note that it wasn't until sales of the iPhone/Pad/Pod started slipping that all of a sudden the lawyers were let off their leashes. That's always an indicator that a company basically has nothing left but to try and cling to relevance as long as possible by competing in the courts instead of the market.

I got home, the mini HDMI cable waiting for me, and ran over to plug it in immediately. Voila!

http://i.imgur.com/Kc8Cvx0.jpg

The 750 says it supports up to 4 concurrent displays, so it might be a viable option for 4, but I know if you're gonna spend the money on 4x 30" 4K monitors you're not gonna need to scrimp on the video card lol...

I hadn't heard of Matrox, but I did help my cousin find a company that sold 2x GPUs integrated with eachother a couple years back. I believe they were GT 430s that were soldered and modified to act as two GPUs on a single-slot PCI slot, and it works perfectly fine to this day for his 3x 27" monitor setup. Can't remember what the company was now, but it was something like $300 at the time. Nowadays it looks like more higher end cards are pushing support for more than 2 monitors, but I'm sure within the next few years it won't be hard to find even basic $50 cards with native support for more than 2.

The new Mac Pro actually supports up to 6 thunderbolt displays, which you COULD go with 4K monitors on if you wanted...Simplified, it would probably be really nice to have one if you had the money, despite the fact that they do look like little wastebaskets hahaha.

Mobile is where it's at. Everyone is leaning toward mobile, and for good reason. Startups that offer mobile apps, SaS and the like are exploding. It makes sense that Apple would start putting more and more eggs into that basket, since it's not going anywhere. Even when mobile devices are more than capable of running intensive, current-gen type of programs, etc., everything is gonna be leaning toward slim and trim anyway. As it is, it's best practice for most web developers to start with mobile responsiveness first and then build on it. So yeah, why not have the end goal be a seamless mobile-laptop-desktop universe?

Looks like the 640 did exactly what I wanted. Thanks again for all the help, it was a great learning experience!

In action: http://i.imgur.com/Kc8Cvx0.jpg