Working whitebox:

Motherboard: Gigabyte GA-H55N-USB3 (NIC disabled, AHCI enabled)
BIOS: F4
NIC: Intel Gigabit CT Desktop Adapter
CPU: Intel i3 540
ESXi: ESXi 4.1
Storage Controller: Onboard AHCI SATA, no onboard RAID on MB.
Disks: 4*1TB Samsung F3 SATA (HD103SJ)
VT-x: Yes
VT-d: No

Notes:
I boot ESXi from a USB memstick from SANDisk (simply installed directly to the USB memstick from ESXi CD setup). I'm running a Nexenta (3.0.3) VM with all disks in a RAID-Z (ZFS) pool to get redundancy for the data instead of going for a more expensive HW RAID. A sweet little ESXi setup in a mini-itx chassi =)