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.
One Nvidia GeForce GTX 680 or AMD Radeon HD 7970 Ghz should be able to run most games at high frame rates on 1080p monitors with settings at very high. Some games may show frame rate stuttering at ultra detail levels, so you'll need to test each game. If you have a high-end, 30-inch display running at 2560 by 1600, you'll need to manage your detail settings more carefully, unless you have a dual-GPU card, like the GTX 690, or are willing to install two discrete graphics cards.
$300 to $380
Cards in this category include the Nvidia GeForce GTX 670 and the AMD Radeon HD 7950. They offer performance that is nearly as good as that of the high-end models, but at a more modest price. If you stick with a 1080p or 1920 by 1200 display with one of these cards, you should be in good shape.
$200 to $300
At this level you may have to start making some sacrifices in detail settings. For GPUs such as the AMD Radeon HD 7870, that means running at "high" rather than at "very high" detail level, and it almost certainly means disabling antialiasing.
You should check each cards features see what interest you more and check current professional reviews of any card your interested in.