Thing is that motherboard is quite old and wont accept any current fx series chip, else I would have recommended an fx6300
This is probably the best cpu and motherboard upgrade you can gethttp://
or, intel option, later on you can up it to an i5http://
Note that the first option has an unlocked cpu which can be overclocked but the second option has a better upgrade path
or, better than both but slightly over budgethttp://
I would personally take the third option as it is much better than the first two (better cpu, better motherboard) and you can up it to a 6300/8320 later on
What cpu do you currently have?