What Goose and r00 said once again. You've got a really nice area for your budget to be in so you can pretty much have all awesome stuff in your rig.
Picking a good brand and model of RAM is important, as it has more impact on speed than a lot of people realize. I'd pick up an 8GB kit since that's the sweet spot for today's gaming rigs; 9-16GB and up is overkill unless you're doing some serious benchmarking, are involved in serious F@H projects or have a need for the extra memory for media/art/music/editing programs. Corsair and G.Skill are in the top three and you can never go wrong with either of them, but IMO the hands-down best memory kit on the market right now comes from Samsung, of all places:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820147096I'd recommend a SeaSonic power supply -- they're the creme de la creme of PSU manufacturers -- but you can't go wrong with a good Corsair unit since the internal components they use for Corsair PSUs are the same as SeaSonic's. They literally come off the same manufacturing belt in a factory. lol
In terms of Intel motherboards to pair with your i5-3570K, ASRock is my #1 favorite Intel motherboard manufacturer right now because they pack all the punch and reliability of other motherboard manufacturers but cut costs without sacrificing quality. In some departments, their components are actually BETTER and higher-quality for less cost.
ASRock Z77 Extreme4:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157293(Though Gigabyte's Z77-UD3H is always a solid choice, too...)
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128544I was looking at an MSI 660 Ti myself:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127696(MSI make amazing fans and the whole card is made of solid construction and components.)
PSU, Mobo, Memory, CPU, GPU aside:
Storage. IMO the best thing you can do for your PC to make it blazing fast is to get a smallish (say, 64GB-128GB) solid state drive and throw ONLY your operating system, browsers, programs and apps -- and maybe a handful of slower games -- onto the SSD and pair it with a second storage unit -- a high-capacity, high-speed hard disk drive (7200RPM, 32mb cache, with 500GB-1TB of space) -- to throw all your files like movies, music, pictures, yada yada, onto it. The amount of space pertains to your own tastes, but make sure it's at 7200RPM and totes at least a 16mb cache.
