Maximum PC

This is the first rig I have ever built so please comment on how I can improve

Processor AMD Phenom II X6 1090T Black Edition
Motherboard ASUS Crosshair IV Formula AM3 AMD 890FX
Memory CORSAIR DOMINATOR 4GB (2 x 2GB) 240-Pin DDR3 1600
CORSAIR DOMINATOR 4GB (2 x 2GB) 240-Pin DDR3 1600
GPU XFX HD-585X-ZABC Radeon HD 5850 Black Edition
PSU CORSAIR HX Series CMPSU-1000HX
Cooling Arctic Silver 5 Thermal Compound
Thermalright Venomous X - RT 120mm
Hard Drive OCZ Agility 2 OCZSSD2-2AGTE60G (100GB)
Seagate Barracuda XT ST32000641AS (2 TB)
Optical Drive Sony Optiarc Black 24X DVD+R
Sony Optiarc Black 24X DVD+R
OS Windows 7 Ultimate
Case Corsair Obsidian Series 800D
Mouse RAZER Mamba
Keyboard RAZER RZ03-00181400-R3U1 USB Wired Lycosa Mirror
Monitor Acer S243HLbmii Black 24" 2ms(GTG)
Fan Control NZXT SEN-001LX Sentry LX

You may want to scale back on the PSU. 1000 watts is overkill. The Corsair 850HX is more than enough for that rig. Also unless you have a need to switch languages on the fly, you don't need Windows 7 Ultimate. Save your cash and just get an OEM Home Premium 64-bit. The only other thing I question is the fan controller. With as many fan headers as there are on the Crosshair 4 (I think there are 8?), is it really necessary? If your primary focus is gaming, as much as I LOVE AMD. The 1090T gets outclassed by the Intel Core i5/i7. A nice 955 black quad core overclocked would make a better gaming rig. Are you looking forward to Bulldozer? If so, don't spend $250 on a motherboard that won't run it. Just some food for thought.

Yeah, no offense intended but you're doin' it wrong. Phenom II X6. And gaming rig probably should never be placed in the same sentence.

The reason for this is that programs have to be optimized for multiple cores, and games aren't.

A thread is a string of commands that a program runs. One CPU core can run one thread. Unfortunately, its not possible to split up one thread among multiple CPU cores, because these commands must be executed in order. Also unfortunately, coding certain programs (like games) to have multiple threads is quite difficult, and right now game developers don't do it. Games older than the Source engine all run a single thread for the most part. So on a 6-core one core will run at 100% while the others sit there at idle not helping. On newer games, you generally see two cores used. That's still only 2 out of 6 cores. A few use three, and a couple four, but so far none use 6 yet.

What all that means is that right now a quad-core that is faster at tasks with less threads (such as the Core i5-750) are going to give much better gaming performance, and save you some money because P55 motherboards are much cheaper than 890FX boards (that Crosshair is a waste of money, motherboards don't have any impact on performance).

I love AMD myself too, but if I was looking to spend that much, I would definitely wait for the bulldozer. I also have the Sentry LX, highly recommend you don't get it. The clock on my was slow, and then eventually it just bricked. Display completely doesn't work now.

Don;t get Arctic Silver either it is dated get the new Tuniq TX-4 (better) or Arctic Cooling MX-3.