It comes down to how much do you want to spend, just like cars, the faster you want to go the more it costs. The prices listed are all in $A which are trading higher than the $US, but we do (for some obscure reason) pay higher prices in Australia for equivalent PC gear than the US.
CASE:
Cooler Master Cosmos II, Black, mATX/ATX/eATX/XL-ATX/SSI CEB,/SSI EEB , No PSU, USB3.0, 1x eSATA - $369.00
PSU:
Corsair AX-1200i Digital ATX Power Supply, 1200w, 80 PLUS Platinum, Modular, 6x 6+2Pin PCIE, 16x SATA, 12x 4Pin Molex, Corsair Link Compatible - $399.00
MOBO:
GIGABYTE GA-Z77X-UP7 MB, Intel Z77, 4x DDR3, 3x PCI-E 3.0, 6x SATA III, 6x USB 3.0, HDMI, D-Sub, DVI, 7.1CH, 2x GBLAN, xfireX, SLI, EATX - $439.00
or
ASUS MAXIMUSV-EXTREME MB, Intel Z77, 4x DDR3, 5x PCI-E 3.0, 6x SATA III, 4x USB 3.0, HDMI, DP, THUNDERBOLT, 7.1 CH, GBLAN, RAID, BT,Extended ATX - $439.00
RAM:
G.Skill 32GB Kit (4x8GB), PC-12800 (1600Mhz DDR3), RipjawsZ, 10-10-10-30-2N, Dual Quad Channel Kit - $225.00
CPU:
Intel Core i7 3770K (3.50Ghz / 8MB / LGA1155 / Quad Core / Overclocking Enabled) - $339.00
COOLING:
Corsair Hydro Series H100i Extreme Performance CPU Cooler with Built-In Corsair Link Functionality - $155.00
PRIMARY HARD DRIVES:
OCZ 512GB SSD, Vertex 4, SATA III, Read up to 560MB/s, Write up to 510MB/s - $459.00
SECONDARY HARD DRIVES:
Western Digital 1TB WD VelociRaptor, SATA III, 10000RPM, 64MB - $265.00
GRAPHIC CARDS:
Gigabyte GeForce GTX690 (915Mhz), 4096MB (6008Mhz) GDDR5, Powered by Dual Geforce GTX680, PCI-E 3.0, Triple DVI, Displayport. - $1,299.00
SOUND CARD:
Creative Sound Blaster X-Fi Titanium HD PCIe, 122Db SNR, 24-bit/192kHz Digital-to-Analog, Swappable OPAmp, 0.001% distortion, EAX® 5.0, Dolby. - $219.00
This was my suggestion to someone who was asking about a system and had a reasonable budget, no idea what came of it as I never received a reply.
Probably appears as overkill at first glance, but it can be pared back in the initial phase and additional drives etc loaded over time.
You could get away with running the two SSD drives (OS on one and FSX on the other, or even a 250GB drive for the OS) but you will certainly find a VelociRaptor (or two) very useful in the future, and yes, I know you could opt for a 2TB drive but I prefer them smaller, the big ones take forever to de-frag, even the 1TB drives take more time than I like.
A single GTX690 is pretty hot stuff, a pair in SLI are really fast but one is a good starting point, and not such a shock in the wallet.
Liquid cooling is a must IMHO, efficient, quiet and space saving.
The Intel Core i7 3770K overclocks quite happily, and 32GB of DDR3 RAM is cheap, so if you are running W7/64bit (another must have IMHO) you can use all of that memory.
Either of the Motherboards noted have plenty of SATA III and USB 3 ports, another big plus.
A sound card???
Not really a necessity but nice to have.