on a 600$ build : it's either X4 750K or Pentium G3258. Though to get an Overclock-wise board you have to pay more with intel.
If 700-800 $ then i would recommend I3-4130 or 4140. around 110$ this will get you nice performance and you save money on board since no overclock there.
800-900 $ AMD FX-8320 will allow you, at 150$, to spend big money on a nice GPU and max any 1080P games.
1000$ + Intel I5 like 4690K
1000$++ Intel I7 for huge powerhouse.