I am planning to DIY a desktop computer. Favorate CPU is E8200 with 1333MHZ, MoBo is Giga EP35-DS3R.
I am now looking for a suitable Graphic Card. There are many good graphic card manufacutures, such as eVGA, Leadtek, Giga, Asus ..... My favorate one is the one with 8800GT
 
I am now seeing eVGA website, too many types of 8800GT cards.
 
The price goes down while the GPU clock speed and the memory clock speed decrease.
e.g., e-GeForce 8800GT KO 512MB    GPU clock speed 675Mhz,Memory Clock speed 19500Hz (269,99USD)  
        e-GeForce 8800GT 512MB         GPU clock speed 600Mhz,Memory Clock speed 1800Hz (239,99USD)  
         
There are also other types, prices vary while speed change.
 
Considering my CPU and MoBo(I will buy 2x2GB ddr2 800Mhz memory), what clock speed is the one well-matched.  
 
 

eh, that doesn't matter at all, PCI-e bus speed is 100MHz and completely separate from FSB of your cpu or memory speeds. So faster is..  well faster. ;D

faster of everything will help speed things up.you can 0verclock you pci-e slot.

^ Agree
 
eVGA is a great brand.
I would recommend going with their cheapest model and overclocking it your self.