I am very close to purchasing the same combo. I too am trying to decide on the memory right now. I am leaning towards the Corsair TWINX pc-8500 5-5-5-15 2GB sticks. I just dont think 4 GB are necessary yet... maybe when Vista comes out but you can always buy the other 2GB later.
I am hoping that the Evga 680i will take advantage of the 1066mhz sticks, if not then probably go with the 800mhz ones.
Which 680i are you going with? I was planning to go with the EVGA that came out now. Any advantages to waiting for the ASUS?