For an amateur workstation machine with some light gaming, it's hard to beat an E3-1231V3 + GTX750Ti on an H97 or B85 motherboard with 16GB RAM. However, if you want something a bit more "professional" then you'll want to install that same E3 Xeon on a C226 chipset motherboard with ECC memory and pick something like a K2200 video card. Depends on how critical it is that you have the workstation drivers for the programs you use, and how sensitive you are to the premise of compute accuracy.
To put things in perspective, the E3-1231V3 performs anywhere from on par up to ~30% faster than an FX-9590 depending on the workload. The E3 achieves performance matching or exceeding the flagship AMD product, while (often) costing less to implement than a flagship AMD chip, and while dissipating about 1/3rd the power.
If you prefer to stay on a tighter budget, i5's and FX-83XX parts are pretty interchangeable in workstation performance, and many AM3+ motherboards support ECC memory (all FX chips do, so it just needs BIOS support), so if you wanted a system with error corrected memory you could accomplish this with an FX-8320/8350 at a lower cost than on the Intel E3.