Which Graphics Card you should buy ?

Someone might suggest Radeon 4650or 9500 GT.Please don't try. Even for running 6600 GT card you need a local PSU with 450W rated PSU. If you try running 9600GT DDR3 or 4670 in a local 350W rated one, then there is a high chance that either ur Card or SMPS will get damaged. Other parts may also be damaged. 

Why go for a Radeon 4650 or 9500 GT. They are under performer card and just buying a 1 GB card won't let u play all the games in good details. You need a good GPU also. 
So opt for Nvidia 9600GSO/GT or ATI 4670 GDDR3 based cards. All of them are available under 5k.
My suggestion is XFX 9600 GSO 768 MB. Remember the brand. This is a special edition card from XFX which is a better performer than other 9600 GT cards. Go for it. Price is around 4.2k. don't go for GSO from other brands.
ATI based best solution will be PowerColor AX4670 1GB. Price is around 5k.

But remember 9600 is a better performer than 4670. But 4670 consumes less power and hence u don't need a very good SMPS to run it.

Hope This Helps :-)