Using antialiasing (AA) is still one of the best ways to improve a 3D image. Antialiasing blends the colors of nearby pixels and smooths the contrast between them. Doing so minimizes the classic "jaggies" effect that you may sometimes see in diagonal lines during gameplay.
GPU makers have implemented increasingly sophisticated antialiasing methods, including ways of blending pixel colors over time. Nvidia's TXAA is one example of this.
SLI (Nvidia) or CrossFire X (AMD)
If you want to run the highest AA levels on displays with resolutions of 1920 by 1200 or larger, or if you want to run stereoscopic 3D, as with Nvidia's 3D Vision, you may have to install two cards instead of one. The two cards are connected to each other via a short data cable so that they remain synchronized and effectively behave as a single graphics card with nearly double the performance.
DVI, DisplayPort, and HDMI
These are ports used to connect monitor cables. If you must connect via VGA--which I strongly advise you not to do--you'll need a DVI-to-VGA adapter. Most retail boxed cards include such an adapter.
DisplayPort and HDMI pose their own challenges. Cards may use mini-HDMI or mini-DisplayPort connectors. If the vendor doesn't include adapters in the box, you'll have to hunt them down on your own.
DVI-Dual Link connections can drive very-high-resolution 30-inch displays, but not all DVI connectors are created equal. Single-link connectors max out at 1920 by 1200, so check the product information if you need more.
HDMI's latest version is 1.4a, and you'll need that if you want to run 3D Blu-ray movies or to run 120Hz monitors in stereoscopic 3D.
DisplayPort is now at version 1.2, and most of its coolest features as yet go unused. DisplayPort 1.2 will permit you to daisy-chain two displays off a single port, but no monitors with DisplayPort 1.2 support currently exist, though they should begin to arrive before the end of 2012.
Like most tech products, graphics cards are segmented by price. Expensive cards tend to be more capable; and less expensive ones usually offer lower performance, consume less power, and are smaller in size (and so fit into a greater range of PC cases).
$400 and Up
The highest-priced cards deliver the strongest graphics performance, but they're also more power hungry. Both Nvidia and AMD have released a new generation of GPUs that are more power-efficient than their predecessors, but you'll still want a good 600-watt power supply to run these types of cards. At the extreme high end are dual-GPU cards, such as Nvidia's GTX 690. You can expect to spend close to $1000 for one of these.
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