Whats the decent-best graphic card that is compatible with my computer?

OS: Windows 7 Home Premium (6.01.7600)
DirectX: 9.0c
CPU name: AMD Athlon(tm) II X4 620 Processor
CPU speed: 2600MHz
Memory: 4096MB
Screen size: 1600x900 (32bits)
Video card: NVIDIA GeForce 9100, 256MB

*Bump*

Can anyone help me please?

:'(