Well it depends on what video cards you use. I usually have one high end CAD/3D card on my system and will put either 1 cheap or 2 cheap PCI cards to run the others. These can be problematic. I have one system which uses two SLI cards which are mated together on the newer PCI express. You definitly want ultramon or some utility you can add task bars to each monitor. There's a lot of added functionality. There are some other ways to go Matrox makes triple head to go. It's a system that will allow you to go three heads in open GL (I think I could do stretched video across all my monitors with this) i'll have to look into it
As for cables they're pretty much just standard. You have either a VGA or DVI coming out of your video card to each LCD. Sometimes you have a DVI that splits into two VGA's. It depends on the card manufacturer. I have different setups on my different systems. You'll definintly have 2 video cards unless you were to do a so a lot of times it's wise to really think about everything you want to do because if you want to add an ATI HDTV card you will have to deal with having to have an ATI video card to use it. Then there are other driver issues, some cards don't work as well together as others.
LCD's are way cheap today so it's an excellent time to go multi monitor. You'll be surprised at how much faster you can work. Especially if you're smart about your GUI, I use windowblinds and the "Black Hole" skin. It allows me a lot of different things I can do with each of the windows that windows standard just doesn't do.
Few good sites to look to get reliable and specific information (from their forums) as to the best hardware to get.
hardocp.com
anandtech.com
arstechnica.com
tomshardware.com