gtx460 is videocard with nvidia GPU inside (Graphic Processor Unit). There is 2 versions of gtx460 with 768mb of video memory and with 1gb. In order to run 3 monitors on any gtx 460 u will need 2 videocards in sli mode. However if u go for ati 5xxx card u will be able to run 3 monitors with only 1 videocard.
nvidia is a company that produces Graphic Processor Units, so does ATI.
Palit, MSI, Powercolor, XFX, PNY, EVGA and many others are companies who manufacture videocards using both NVIGIA and ATI GPUs. All of them make some great videocards.
What is your purpose? Do u want to play games on 3 monitors, or u need them for multitasking?
Nvidia and ATI design graphics cards, where as Palit, MSI and other companies manufacture them ( different manufacturers add different toppings too, like adding ketchup or hot sauce )
So if u want to use 3 monitors at the same time, 5xxx series designed by ATI has the capability to use 3 monitors at the same time. The GTX 460 which is designed by nvidia, doesnt have the capability to use 3 monitors at the same time.
The 5830 and 5770 by ATI has the capability to use 3 monitors ( the feature is called "Eyefinity" ). The 5830 is the closest competitor to the GTX 460.
But if u want the gtx 460 really bad and u also want to use 3 monitors, u need two gtx 460 graphics cards, running together ( Which is called SLI, coupling same graphics cards together so they offer better performance ) Careful though, coz SLI'ing two graphics card could be very alien to you.
So you are better off buying a 5830. Which manufacturer? i dont know!
HDMI is a type of monitor to videocard connection, its not must to have, it depends on what kind of monitors u r going to use.
if u r not going to play games or run any graphically intense applications even cheap card like this will do the job: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
But keep in mind that if 1 of the monitors u r going to use doesnt have display port with this card u will need display port to vga adaptor.