A couple of points:
Abit already offer a PCI-e socket 939 motherboard. It also has what we should probably start refering to as "legacy PCI" slots by way of having a an onboard PCI-e legacy PCI controller.
To recap, if you use the legacy PCI slots, they then go to the legacy PCI controller, which is a PCI-e device, so it then goes to the PCI-e controller, and then you get linked to the CPU/RAM/whatever.
This may introduce a bit of extra lag, but it's unlikely to be noticeable as legacy PCI goes at a snail's pace compared to PCI-e.
Here it is: http://www.abit-usa.com/products/mb/pro ... &model=215
As has been mentioned, there are now S939 90nm A64's on the market. Availability is still rather limited though, and it's probably worth waiting a while. Why? Firstly demand is way higher than supply at the moment - this pushes the price up. Secondly, AMD are still "creaming the market" with the S939 chips, especially the newer 90mn parts - this means they set high prices, wait for everyone who is willing to pay the higher price to buy, then drop the price to it's final "mainstream consumer" level. Give it a couple of months and I imagine they'll come down.
Be aware that if you get a board that has no legacy PCI support (if and when one becomes available), there are VERY few PCI-e expansion cards around right now. That means it'll be hard for you to find things like firewire cards, sound cards, tv cards, network cards etc in PCI-e format. So if you get a PCI-e board I'd make sure it has a legacy PCI slot or two.
Just some tips.