P45 boards are rock solid. You really cant go wrong with it, at all. Be it ASUS, MSI, Gigabyte. They are all good.
As far as the Nvidia chipsets go....its really a coin toss. And I really mean that. You have about a 50% chance of getting a board that actually works, in terms of memory issues and massive voltage issues with overclocking.
Check newegg.com for prices and parts. They have the largest selection of everything.
Intel Core 2 Quad Q9550 12MB
Corsair XMS3 DHX 2 x 2 GB
ASUS EN9800GTX+/HTDP (512 MB)
Antec Performance One P182
Corsair CX400W PSU
ASUS P5Q3 Deluxe/WiFi-AP @n Motherboard
Western Digital Raptor 150 GB, 10000 RPM Disk
Hitachi Deskstar 7K1000 1TB Disk
Scythe Ninja PLUS SCNJ-1100P CPU Cooler