Actaully, both the ASUS SLi and Neo4 SLi board are bad OCers, but in general, stay away from ASUS's nForce4 boards... they are BAD NEWS (says me, a person who had their original 3,200 dollar SLi system blow up from one of those evil things) The Neo4 is very stable and a good board, but it OCes poorly when compared to these 3 boards. I would recommend these in order of their listing, top board being the best, and so on.
ABIT FATALITY SLi A8N Ultra
Out of stock for now sadly, but it will be back in. Do an AUTO NOTIFY. However, this board, and the other ABIT board below are the ONLY boards currently sold that are DUAL CORE ready out of the box without having to hastle with a BIOS flash, which BTW, with ABIT is dreadfully EASY!
DFI's nForce4 SLi Ultra Board
Th is board is also VERY VERY GOOD. It is rock solid and OCes probably the best, but can be tedious to configure and setup properly.
WITH BOTH OF THE ABOVE MOTHERBOARDS, you need to get good RAM to use it with. Recommended RAMs are Mushkin's REDLINE PC4000 DDR500, or OCZs VX DDR500 PC4000, both running on 3.3V!
Here is the lower priced option to this mess, but still a VERY GOOD BOARD:
Ignore the second review about SLi not working, ABIT just released the BIOS Rev. 16, which is AWESOME and allows for HUGE OCIng. THis board is not quite as good as those others, but better then both the Neo4 Plat and the ASUS A8N Sli.