Here's my current system (mobo, CPU, RAM, GPU, & PSU) and Newegg prices (excpet for the PSU):
AMD64 3500+ Vencie >$200
Asus A8N-E $100
Corsair XMS 2x1gb RAM >$200
Sapphire X1900XT $430
PCPower&Cooling510SLI $200
Total comes to $1130, but you can always opt for an Antec for about $100 less. The only thing I have to warn against: the chipset fan on the A8N-E will probably wear out, and you cannot use a heatsink with the X1900XT at the same time. I would recommend shellling out the $50-75 extra for a mobo with a heat pipe instead (just make sure you have adequate air cooling in your case).
My system runs very well, and I've noticed a substantial increase in framerate from my nVidia 7800GTX 256mb card. I run my games at 1920x1200 when possible, so if you're running at lower resolutions, you might not need such a hefty videocard. Either the X1800XT or the 7900GT should suffice and save you a few bucks to boot.