Please go through this link. I am sure you would get many options to choose . Then pick your mother board as per your Budget. You can buy P5K series Asus. I personally use S3210SHLC . Do not buy this one coz ESX detect only 1 NIC card & it is also costly one. Apart from that you have to flush the BIOS . This board has got inbuilt 2 NIC cards.
If yuou are looking for a Intel Server board http://www.intel.com/products/server/motherboard/index.htm
The ESAA pages can give you a lot of information on recipies to make sure every thing works http://www.esaa-members.com/pages/solutions/virtualization
But if your not looking for the best server boards (shameless plug) http://www.vmware.com/resources/compatibility/search.php
list all the manfactures who have ESX certified boards.