Yeah based on the latest Tom's monthly article "best gaming CPU for the money", the Phenom-II X4 still receives a good recommendation. Some years ago the Intel i3 was recommended before it in the same price range, but with more and more games supporting more than two cores, now it's the Phenom-II X4 that gets the recommendation. I agree with Giovanni, it's still a very decent gaming CPU, so no need to change it yet.
Even your video card isn't that bad, so unless you're having some performance issues when gaming, you could postpone any upgrade to later and save even more money. But if you need to replace something I'd go with the GPU. In your price range, a Radeon 7870 or the new GTX-760 maybe?