The DDR4 EUDIMM Memory I've Been Buying The Most
There still isn't a big selection of DDR4-2133MHz ECC Unbuffered (EUDIMM) memory as needed by Xeon E3 v5 systems, but the best value I've found and have been using it as my go-to memory for such systems is the Kingston ValueRAM 4GB 288-Pin DDR4 SDRAM ECC Unbuffered DDR4 2133 (PC4 17000) Server Memory Model KVR21E15S8/4HA.
Getting two sticks of this Kingston KVR21E15S8/4HA is enough for most of my benchmarking systems with not needing more than 8GB for many of these daily benchmarking systems for LinuxBenchmarking,com, OpenBenchmarking.org, etc.
The memory is a better deal than the limited number of other DDR4-2133MHz EUDIMM offerings available from major Internet retailers. I haven't had any problems with the eight sticks of KVR21E15S8/4HA that I've bought thus far and have worked fine on all the Skylake Xeon motherboards I've tested, including the ASUS E3 PRO GAMING V5, ASRock Rack C236M, MSI C236A Workstation, and ASRock E3V5 WS.
If you are interested in this memory you can find it for $25 USD per stick from our friends at NewEgg.com. The same memory also appears to be offered via Amazon.com but it's not Prime and is priced at $31. So overall I'm happy with the Kingston KVR21E15S8/4HA for being low-priced but reliable DDR4 EUDIMM memory.