Use Kingston KVR16E11/8 modules and it will work. Be sure to use a Xeon with 1600MHz support. 8GB sticks are $36ea on Newegg brand new, or $25ea on eBay in sets of 4 from seller holltronic2 who I've ordered from before reliably. Also, these DIMMs have temperature sensors which is pretty neat since you can see it in ESXi or AIDA64.
Per Supermicro, the board is only spec's for 32GB, hence the 8GB DIMMs. Also, those e3 Xeons only address up to 32GB of RAM per the Intel spec.