Just in case someone is interested in another working "whitebox" config for ESXi 5.1 here is one I've just built for my home lab about 2 month ago.
This is a basic build so it hasn't got a decent hard disk RAID card installed but that can be added later, I just wanted to see what basic config I could get going first and then start adding better hardware to it as more money becomes available 
CPU: Intel Core i7-3770 3.4 GHz, Socket 1155
Memory: 2 x Kingston ValueRAM KVR16N11/8, 1x8GB, DDR3-1600, PC3-12800, CL11, DIMM
Motherboard: Intel DQ77MK Motherboard, Socket 1155, Intel Q77, 4xDDR3, 1xPCIe-16, 1xPCIe-1, Firewire, VGA, DVI, RAID, M-ATX, OEM
PSU: Enermax NAXN ENP650AWT, 650W ATX PSU
Optical drive: Samsung SH-222BB DVD Writer, DVD 16R/22W/8RW, CD 48R/48W/48RW, Internal, SATA
Case: NZXT H2 Classic Silent Midtower Chassis Black
HDD: Any sata drive you want to use, just no RAID until an addon RAID controller card is installed.
At first I was put off from using a Micro ATX board for a server type machine but it turned out to be a great motherboard to use, both onboard network cards are working for me in ESXi 5.1. All I had to do is use the ESXi-Customiser and add a driver for one of the on-board network cards into the ESXi install ISO image, the 2nd card was already supported by ESXi 5.1 natively.
This page lists exact instructions on adding the network card driver into the ESXi image:
http://www.ivobeerens.nl/2011/12/13/vmware-esxi-5-whitebox-nic-support/
The only other thing I had to do to get ESXi to install was to flash the motherboard BIOS to the latest version, without a BIOS upgrade it would not boot properly.
Also that motherboard has space for 4 RAM DIMM's so I have the ability to add another 16GB of RAM to this server at a later stage if I need it.
(The board supports a maximum of 32GB RAM)
I know in earlier posts many people are using Asrock motherboards because they claim to support VT-d but here in NZ Asrock don't have a good reputation and I prefer to avoid using an unreliable brand. My friend used to sell Asrock in their computer shop and had many many failures, so much so that they actually withdrew that product brand all together. Maybe it has gotten better since but I didn't want to risk it.
Btw, I went for a Q77 board instead of a newer Z77 board because Q77 is clearly listed as supporting VT-d, but for Z77 there seems to be varied support between different motherboard makers. It just didn't seem 100% to me so I went with a sure choice.
Hope this is of use to someone here,
cheers,
G.