well go for the DFi mobo, it's much better than asus
also, are you going to actually go SLi (use 2 gfx cards)
Antec TruePower, OCZ Powerstream, Thermaltake Purepower...
TT purepower is 20pin, the 24pin ones aren't good enough for 2 gfx cards
only the 550W trupower is good enough for SLi (antec)
OCZ powerstream is good; modstream is too weak for SLi