Thanks for the advice, the Gigabyte motherboard looks good, and you guys must be mind readers because I ordered an eVGA 8800GT yesterday (going to try it out in my current system while waiting for the CPU).  I've used eVGA's step-up program before (7800GT to 7800GTX in my current system, a couple of years ago) so I'm a loyal customer with them now.
The motherboard and memory options are the most confusing to me, with DDR2, DDR3, and the various chipsets that are available.  My budget can go pretty high, but I'm interested in building a fairly quiet computer with great performance as well, so things like passive heatsinks and low power consumption (this is why the 8800GT caught my attention) are helpful, especially when considering that I'm going to be trying to get a Quad core running in this system.  My power supply will probably be some mid-powered (500-600W) quiet unit (Seasonic or one of the variants).
In my current system I have lots of quiet 120mm fans running at very low speeds, controlled by a software fan controller, so a motherboard with lots of controllable fan headers is going to be a good thing.  I like my system extremely quiet when I'm not gaming (usually listening to music and surfing the web), but I don't really care how loud it gets when I'm playing 3D games (my attention is usually not on the fan sound at these times).  
