Well, what are you using currently? If you buy a new Cpu, you'll most likely need new Ram as well(and definitely a new motherboard). So, without worrying about cost, I'd get an Intel 4670k Cpu(or 4770k if you play one of the games that takes advantage of Hyperthreading like Crysis 3), I'd get an Asus Z87-Pro motherboard or AsRock Extreme6 Z87, and I'd pick up 2 x 4gb sticks of DDR3 PC1600/1866 Ram(depends on what happens to be on sale at the time). Look for g.Skill, Corsair, Crucial, GEiL, Patriot for brands.