What is the best graphic card for ASUS P5KPL-VM-MUSTEK-SI, Chip-set: Intel P35/G33/G31, CPU: Intel Core 2 Duo E6550 @ 2.33Ghz 2.33Ghz? Price doesn't matter.
Well, your CPU is old and slow by today's standards. I would go with a HD 7750 or HD7770 depending on what PSU you have.
Check to see that your motherboard actually has a PCI-E 16x slot first.