the motherboard? it depends on the CPU
assuming you're gonna get an Athlon 64, which is currently the best CPU for gaming, I would suggest the DFI NF4 Ultra-D
second to that would be the MSI K8T Neo 4
then the Abit AN8
or if you're going AGP (which I wouldn't recommend now, PCI-E is the future) I would say the MSI K8T Neo 2, or the Abit AV8 3rd eye
DFI, MSI and Abit are pretty much THE brands of motherboard for socket 939
as far as video cards go, the 7800 is a really good card, but expensive.
ATI is going to make a new card, which might be better, but a lot of us are just speculating. a lot of us haven't made a judgement on whether we like ATI's or Nvidia's new card best, because we haven't seen what ATI's is like