Here's a handy reference guide that takes into account the latest additions to the GPU landscape from AMD and NVIDIA. This table should be handy if you're buying a discrete graphics card - whether it's for an entry level, mid-range, or a high end gaming rig.
The world's fastest graphics cards - the GTX 590 and the Radeon HD 6990 are available in India, but unless you're a hardcore gamer or a megalomaniac, we'd recommend something less expensive from the GeForce 500 series or the Radeon HD 6000 series.

Older graphics cards can be probably picked up for a bargain, to see how they stack up against present generation cards, here's a comprehensive Graphics Card Hierarchy Chart, published by Tom's hardware. It bottoms off to 10 year old chipsets like the Riva TNT and Rage 128! Anandtech publishes and updates an abbreviated version with USD prices, check it out to get a summary of what's available this buying season.

Via: technoholik,AnandTech