the second is optional.
for video cards, there's not much diff between manufacturers until they start deviating from the reference design or applying a factory overclock. most 8800gtx are identical except for a water cooled variant. i suggest you go with best price/game bundle.
as for motherboards, there's much more distinction. check out the enthusiasts sites like hardocp.com, hothardware.com, and anandtech.com for motherboard reviews to help you decide.
I'm an extreme gamer, planning to build my own PC but I'm having problem choosing the right motherboard. I'm interested in the nVidia nforce 680i Can a SLI motherboard run a single Nvidia Geforce 8800GTX instead of two?
Also, is there a difference between the manufacturers such as MSI, Asus, BFG, eVGA and etc for the motherboard and graphics card?
Please help me with this issue?