Depending on what are you planning to do with your computer... If you're doing recording,rendering and streaming then you should go with something like AMD FX 8350 or AMD Phenom II X6 Black 1100T.
Nowadays games wont use more than 4 cores (well maybe some mmo games would because they're heavy CPU intensive). People on the internet saying that next-gen consoles (x86 platform) will use up to 8 cores on next-gen games, meh you never know...
Will be perfect if you could give us your budget (<money you planning to spend).
Anyway here's my suggestions.
CPU: Intel Core i5 3570K - (~200e) - It's the default/recommended choice for gaming build also i guess you're not planning overclocking so the non K version should be fine for you.
GPU: ATI Radeon HD7950 - (~300e-280e) - I'm not really fan of ATI but dude with 3GB Graphic memory and free game bundles in this price, you gotta love them.
MOBO: Asrock Z77 Pro3 - (~80e) - Buying a good motherboard for better system stability :)
PSU: Corsair Builder Series CX500 80Plus Bronze - (~60e) - Always buy certificated power supply for better results under loads/stability/protection.
RAM: Kingston HyperX Blu 4GB 1600MHz DDR3 x2 - (~40-35e) - Meh, i like them.
HDD: Seagate Barracuda 1TB SATA HDD - (~60e) - Nothing specially. Your choice.
CPU: AMD FX 6300 - (~100e) - Why 6 cores ? We all know windows is running background threads so the cores wont be wasted. Also i think is good deal for ~100e because you get the similar performance with i5 3570K when it comes to multitasking.
GPU: ATI Radeon HD7870 - (~190-200e) - Bundles bundles bundles... You can check GeForce 660GTX for similar performance/price.
MOBO: Gigabyte GA-970A-DS3 - (~80-90e) - Decent motherboard.
PSU: Corsair Builder Series CX500 80Plus Bronze - (~60e) - ^
RAM: Kingston HyperX Blu 4GB 1600MHz DDR3 - (~40-35e) - ^
HDD: Seagate Barracuda 1TB SATA HDD - (~60e) - ^
I didn't add PC peripherals such as mouse/keyboard etc.
Why AMD ATI and not Nvidia ?
More Memory, less money, tons of game bundles, not so far from Nvidia.
Also nvidia launched geforce 700 series, it was just a 'revamp' of 600 series nothing special wider memory bus meh still using only 2GB graphic memory meh..
AMD & INTEL:
What the difference between these two on games ? (for example 6300 vs 3570k 'n same graphic card).
Depending on game will be more CPU intensive? With Intel you may win 6~13FPS.
More GPU intensive ? With AMD you'll lose 3~6FPS.
Is it worth to pay 100E more and gain 15~10 FPS more ?
In my opinion NO.
This is just a version of default clocked 5GHz FX 8350 that made for marketing/advertising and GWR nothing special. Buying a stock 8350 with evo 212 and you'll able to get in his territory.
Also keep in mind many benchmarks software/sites are sponsored by Intel since he's dominating on marketing/advertising ;)