I recently built a computer for productivity and gaming, its detail are as follows:
-Processor: AMD Phenom II X6 1075T @ 3.0GHz (6-core).
Better than the i7 in my opinion.. simply because it's faster, and cheaper.
-RAM: Corsair 8GB DDR3 1333MHz (4x2GB).
Decent amount of gaming RAM.
-Motherboard: ASUS M4A78T-E.
Not the best motherboard, but it isn't bad either, it'll handle most of what you throw at it.
-HDD: 2TB WD Serial-ATA Internal
I don't care much for Western Digital, but this was a deal I couldn't pass up; got this for $20.
-Graphics: 3D-Enabled Cyclone GeForce GTX 460 1GB GDDR5 VRAM.
Amazing graphics. I can play Call of Duty (MW2) at 100FPS minimum.
-Monitor: 19" ASUS, 1440x900.
It's a monitor... what can you say?
-750W 'Ultra' Power Supply.
Maybe a little overkill for the system, but I have room for expansion.
-Blu-Ray Player.
Who doesn't love Blu-Ray?
-Windows 7 Home Premium 64-Bit.
The best OS on the market.
This computer is lightning fast. It has a Windows Index score of 7.5 (7.9 being the best) in each area but the hard drive (which got a 5.4). Windows leaves the 7's for those with large SSD drives, or RAID drives. You can build this PC listed about for about $900-$1000, but if you want to buy it, it's gonna be about $1500-$2000 USD, depending on where you buy it.