there's a few boards competing for the top OCer status. the Abit NF7-S is the top contender, the Asus A7N8X is very close to the NF7 but falls short on CPU voltage (1.85 limit), the Epox 8RDA3 has all the features it needs but i haven't heard much about it (good or bad). Gigabyte had a Nforce2 board now too but it's still pretty new so there's not much real world testing done yet that i know of.
if i were to buy one today it would be the NF7-S revision 2 (the revision 1/1.1/1.2 had a major problem with bios corruption, best to stay away from those if possible).
on the other hand, if your not shooting for a max overclock then i would look into the Asus A7N8X Delux. it has more bells & whistles then any other Nforce2 board currently on the market.