Getting the best graphics card for my pc

[mark figg]

Hello,
im looking for the best graphics card for my pc
computer spec
CPU 2.20 gigahertz AMD Phenom 8550 Triple-Core
Mother Board: PEGATRON CORPORATION VIOLA 2.03
Ram3584 Megabytes Usable Installed Memory
Vidoe cards NVIDIA GeForce 9300 GE

 

[perfectblue]

Power supply make and wattage ?

 

[mark figg]

LITE ON model ps 5301-08hf dc output 300w