I used a Gigabyte GA-K8U-939 ULi M1689 for my son's rig since it was really cheap - and it performed great as a bonus w/ the 6800gt.
I would probably take that over the Gigabyte GA-K8NSC-939 Nforce3 for both the lower price, and the higher HT bus speed (the ULi is 1Ghz HT and that one is 800Mhz HT) although I have seen this ECS NFORCE3-A939 (1.0A) which is really really cheap and has the 1Ghz HT - but not such a big ECS fan...
There is the famous ASRock 939Dual-SATA2 ULi M1695 which has both AGP and PCI-E which gives you the option to upgrade, probably the best choice since you have a nice fast CPU...
Uli chipset is more stable... but must check for this Abit product ,as this model was design in some dark period of Abit (financial problems) so may have some poor savings on project...
I'm very happy with my MSI Neo2 Platinum with an Athlon 64 3500+ and the same graphics card you have. If you can find it anywhere it's a very good mobo