Hardware Recommendations:
CPU:
An i5 2500k or equivilent later gen is about as good as it gets without investing some serious money into 6/8 core intel procesors.
Motherboard:
Motherboards don't really effect framerate in single card systems so you don't have to spend a lot out on a motherboard unless it's for features you actually want/need. You could use the money on something much more important like a better graphics card. Personally I would just go for whatever has the most responsive drivers since that's where 99% of your issues will be.
Graphics Card:
The 900 series Nvidia cards offer insanely good performance for the money but they can have input lag issues which come and go with driver updates though this isn't really as much of an issue as it sounds.
Ram:
Ram isn't really too much of an issue, just get 8 or 16GB of 1600/1866mhz ram with the lowest timings possible (around CL9).
Storage:
An SSD will dramatically improve your overall experience, especially if you're a power user. They improve loading times and greatly reduce situations where you computer grinds to a halt while it waits for your harddrive to catch up. Samsung generally make the best price/performance drives and they pick the best chips from the ones they manufature to make their own SSDs.
Peripheral Recommendations:
Monitors:
After using a 144hz monitor for over a year now I can't even think about moving back to 60hz. Subiquently I won't suggest anything else.
Mice:
It's hard to recommend a mouse because there arn't many "good" ones. The Ninox Aurora was designed by quake players to be the ultimate gaming mouse so hopefully it lives up to it's reputation.
The Zowie FK1 might also be a solid choice.
Mouse Mats:
Try to get one that's atleast 45cm wide, a deskpad is normally a good investment as they cost about the same.
Notable mouse mats include:
Puretrak Talent (Owned and used for a looong time, it's pretty nice)
Steelseries Qck+ (Owned one, can't remember liking it much)
Steelseries Qck Heavy (It's a Qck+ with a thick backing on it like the other mouse pads in this list)
Zowie G-TF (Owned and used it for quite a while, there are two versions mine had a lot of friction)
QPAD FX-90 (My current mouse pad, it's like a giant puretrak talent but not as stretchy)
QPAD UC-90 (The uncoated version of my pad, it's probably a better choice)
Tighter weave mouse mats generally have more friction so bare that in mind.
Headphones:
Try to get headphones instead of a headset since they generally contain much better quality speakers and subsiquently sound much better.
My Personal Setup:
http://www.overclock.net/lists/display/view/id/5434346
Computer:
Intel Core i5 2500K
MAXIMUS IV GENE-Z/GEN3
GIGABYTE GTX 660ti
Corsair XMS3 2x4GB 1600 CL9
Creative Sound Blaster Zx
Samsung 830 128GB
Samsung 840 1TB
Peripherals:
BenQ XL2411T
Mionix Avior 7000
Philips Fidelio X1
Qpad MK50
Qpad FX90