Power Supply: 1x Corsair 600w PSU for $45, 1x EVGA 6002 PSU for $50. 1200w for $95. Also, raidmax has a 600w PSU for $40 after rebate, but some people want modular PSUs.

Dual PSU adapter to hook the 2 together, $10

Motherboard: Z87 Fatality, $105. I have this one in one of my builds and a build I did for a buddy of mine. Both are rock solid, and they'll give you room to grow. They have SEVEN pcie slots, so it'll be a while before you need to add another entire rig to your setup. Also, they have 3 full PCIE slots, so you won't need to buy any risers (which you don't have listed in your original build). I would suggest using the top and bottom full slots. The motherboard you have listed is very weak, as far as upgrade potential goes, and just overall performance.

CPU: Intel Celeron G1820 Haswell 2.7GHz, $50. I would suggest this over a sempron build. My first build used that sempron processor...and it is sloooooooowwwwwwwww. I know, I know, speed isn't a big issue in mining, but it makes it frustrating for me that it takes almost a full 2 minutes to get all my mining scripts running. Using that board and this CPU in my 2nd build was a completely better overall choice, imo.

Hard Drive: ADATA 64gb SSD, $50. Skip the laptop hard drive and get an SSD for barely twice the price. The speed increase it totally worth it, imo. Also, if in a year you decide not to mine, that SSD will have some resale value, or at least you can use it as a secondary hard drive for your desktop

Memory: Team Elite 8gb, $60. I found that my hash rates actually went up a little bit when I went from 4gb to 8gb of ram. I would also every now and then get "out of memory" errors when mining with 4gb.

GPUs: PowerColor 280x $329 each. I would spend the extra $20 each to get these cards, since they're already factory OCd to 30mhz more than the VisionTek cards. If the worst case scenario happens and you get 2 VisionTek cards that can't OC (factory locked, or the chips just can't handle it), then you're stuck with the bare mininmum hashrate. On the other hand, even if worst case happens with the PowerColor cards, you're going to be hashing faster than you would have on the VisionTek ones.

So, that's my 2c. Take it or leave it :-)