$2K is a very large budget for a gaming PC.
We could waste a big chunk of your money in a hurry if we went with LGA2011 and X79:
$288½ Asus P9X79 ATX LGA2011 motherboard
$600 Intel Core i7-3930K LGA2011 processor
or $1050 Intel Core i7-3960X Extremely Expensive LGA2011 processor
Let's be sensible enough to stick with LGA1155 and Z68:
$205 Asus P8Z68-V Pro/Gen3 ATX LGA1155 motherboard
or $188 Asus Maximus IV Gene-Z/Gen3 micro-ATX LGA1155 motherboard
$320 Intel Core i7-2600K quad-core hyper-threading 3.4 GHz LGA1155 processor
or $230 Intel Core i5-2500K quad-core 3.3 GHz
or $300 Intel Core i7-2600 (if you need to run virtual machines)
or $370 Intel Core i7-2700K quad-core hyper-threading 3.5 GHz
4 GiB DIMMs of PC3-12800 memory are priced very attractively. Faster or larger DIMMs are more expensive.
$92 4x4 GiB PC3-12800 G.Skill F3-12800CL9Q-16GBSR1 (DDR3-1600, CAS 9, 1.35 V)
or $78 4x4 GiB PC3-12800 Patriot PSD38G1600KH (DDR3-1600, CAS 9, 1.5 V)
or $150 2x8 GiB PC3-12800 Crucial BLS2KIT8G3D1609DS1S00 (DDR3-1600, CAS 9, 1.5 V)
or $120 4x4 GiB PC3-14900 G.Skill F3-14900CL9D-8GBSR (DDR3-1866, CAS 9, 1.5 V)
or $150 4x4 GiB PC3-17000 G.Skill F3-17000CL9D-8GBSR (DDR3-2133, CAS 9, 1.65 V)
Radeon HD7970 is the best graphics card on the market today.
$568 XFX Radeon HD7970 FX-797A-TNFC (925 MHz)
or $608 XFX Radeon HD7970 Black Edition FX-797A-TDBC (1000 MHz)