If you already have a good PSU (not the local ones like TechCom, INTEX yada yada yada), you can go for 9600GT. But if can expand on the budget, go for HD 4850 Palit... I've just ordered both the PSU and HD4850...
If local PSU and 5k budget, you can get down to 3.5k and probably get XFX 8600GT 512 DDR3.... it worked with local PSU