As a starting point, I'd recommend the Haswell-E i7 5820K. 6 cores on the X99 platform, similar to the Xeon E5 16xx v3s but cheaper, unlocked and without certain server features, it can currently be purchased at U$320 if you live near a microcenter, and U$390 if you don't. The clock speed can be increased, through you shouldn't expect much above 4.5 GHz.
Haswell-E does not pack a stock cooler, and it's recommend to spend a bit to get a big, tower air cooler. The Cryorig R1 Ultimate is U$90 at newegg, and is a decent performing 140mm cooler.
If you want a mid range motherboard and don't need any special features, the ASUS X99-A/USB 3.1 has a combo deal with the 5820K. Take a kit of CORSAIR Vengeance LPX 32GB (4 x 8GB), fairly low latency, and you can later drop another kit in for 64 GB.
The 2 TB Seagate Barracuda is a good low cost HDD for mass storage, and if you want, you can also get a SSD for fast boot times. I'd recommend the OCZ ARC 100, 240 GB if you just put the main OS (Hypervisor if type I) on it, 480 GB if you want your VMs' VHDs on it as well. The ARC 100 is a MLC SSD with decent performance for the price, though it is a bit slower than the 850 EVO, it's also cheaper, and the difference will likely be only around 4-5 seconds in boot time.
Since there isn't a big power hungry graphics card, a 550W PSU should be fine. My suggestion is the Fractal Design Edison M 550W. It's a Seasonic made, semi-modular, 80+ Gold PSU, with mostly Japanese capacitors. It is out of stock at the moment though.
Finally, the case, I'd recommend the Fractal Design Define R5, a reasonably spacy ATX Mid-Tower, that has good airflow while still being super quiet. You can get the windowed version for $10 extra, if you want to see inside your computer.
Total is about $1400 USD, from newegg.com, which is about the same price as the Motherboard (incl SoC) + RAM for the option by Journeyman Geek. The Haswell-E 6 core should be more than enough to keep all your VMs happy. If you want to overclock, 4 GHz isn't hard to achieve. Note that Broadwell-E should be out soon, and you can get that if you aren't in a hurry.