Something like a Supermicro
X9SCM-F would probably work, just keep in mind that you might have to manually add the driver for the 82579LM nic (if I remember correctly the 82574L NIC is supported natively) with ESXi. If you google the NIC and ESXi, I am sure you will find a tutorial probably even on this forum.
If you do not want to deal with manual driver installation, the X9SCM-iiF might be a good alternative as it has replaced the 82579LM with a 82574L NIC.
There are a few extra models from Supermicro that might be interesting for you, you could cross reference this "
list" with what you can find on eBay. From what I can see on the "list", the difference with mATX boards is mainly chipset (and thus no. of SATA 3 ports), IPMI functionality (-f) and whether or not it uses 82574L + 82579LM or 2x 82574L.