Depends on what else you're buying/using. I will say that the Athlon X4s aren't worth it, but the Athlon II X3s are. The X4 6xxs aren't very good gaming CPUs, as that fourth core takes too much away from the clock speed. Games wil do better with the faster clock and fewer cores of the X3s. Also, the X3s can potentially unlock a fourth core, making them equal or better than the more expensive X4 6xxs. So the choice should really be either the X3 4xx or the X4 955.
Like I said it, it depends on what you've got already. If you haven't bought a video card yet, it would be better to buy the X3 and put the extra $75ish towards a larger GPU. If you already have the GPU, then you'd do better to get the X4 955.
Of course, if you have nothing, and a total budget for the machine of $750+, you'd do best to wait until Sandy Bridge is re-released and use the i5-2500K.