Core i3 4340. 16GB DDR3, Intel 180GB SSD boot drive, 4TB Seagate hard drive, 120GB Samsung 850Evo as an ssd cache + ready start drive + virtual memory drive.
I used to use a 6 core Phenom II running with ECC memory, but I decided to degrade in size and power consumption to mini-itx. The system runs faster, fits easily under my desk, and does pretty much everything I used to do but faster and with lower noise. Sometimes I run into a memory limit on VMs only having 16GB of ram, but it's generally workable.
Also, I'm using Intel's ssd cache with a Samsung 850 Evo drive and it really makes HDD performance fly, which makes a huge difference for usability in general.
In Crystal DiskMark using Intel's ssd cache, my harddrive does >500MB/s R/W Q32T1 sequential, > 200MB/s R/W 4kQ32T1, >400MB/s sequential, and ~30MB/s / 50MB/s R/W for 4k random.