I'm also looking for a new motherboard and have landed on Gigabyte, although I haven't decided if I'm going to take the plunge for X38/X48 or wait for the P45 boards to come out. Gigabyte use high quality components, and they are particularly good at minimising power consumption. Asus are also very good, and I've buildt a number of PC's with MSI boards. At the moment though I prefer the Gigabyte ones.
The gigabyte P35C DS3R is a great motherboard, but next to the Asus P5KC it hasnt got an advance design as the Asus has a few more sockets at the back, Asus also has heat sinks on 3 bits of the motherboard, gigabyte has it on only 2.
But gigabyte has 8 SATAs and better placed IDE slot, RS232 port and Parrallel printer port where as P5KC hasnt but has more USBs built in + 5 SATAs and a badly placed IDE slot............... its horses for courses and it up to you to work out what you want.
I chose the P5KC and i dont regret it, i dont need the extra SATAs (as my last AMD motherboard could only support 4 IDE drives so I'm use to having this many drives), the P5KC with 5 SATAs + 1 IDE can support 7 drives so it matches my needs
If had to get another motherboard i may choose the gigabyte......... there's no real difference between the two.