I personally always use Asus. I used other boards in the past but Asus always seems to come out top or very near the top in comparative tests. If your going with DDR Ram I like the look of the new Sis 648 chip. Its the most up to date chip suporting all the latest features. VIA always seems to have compatibility issues. As for AGP8x no games will even come close to needing this amount of bandwidth. I don’t think any really use AGP 4X to the max. I supose its good future proofing but by the time its needed newer beter chipsets will be out. There are a few good hardware sites that have looked into this, Tomshardware, Anandtech to name just two, there will be others if you look.
If your using a P4 then you need the bandwidth of DDR400 or higher when it comes out or your strangling the cpu. The cpu has to cycle because slower memory can’t keep up with it. Thats why RDRAM is best for P4, more so now the faster 133FSB (quadpumped 533MHz FSB) are out. I’m looking around to upgrade but its a tough choice at the moment with Intel backtracking on RDRAM. The only new chipset they release, the 850E is only different from the 850 because it supports the faster FSB. It has no support for usb2 or serial hard drives or AGP8x or any new technology.
Sorry if this confuses the issue but the motherboard is the heart of the system and is one of the most important choices as it dictates the rest of the system. I know you can buy addon cards to give usb2 etc but they just take up pci slots so its better to buy a motherboard with the technology built in.