Wow, that is a bad lot of choices there.
FYI, the 9500GT and the 8600GT have the exact same GPU core.
As long as they are clocked the same and have the same amount/type of memory, they will perform the same.
That is to say that neither will give you an adequate gaming experience.
With the two choices you present, assuming the core/shader clocks are the same as they are not listed, you are SOL either way. The 9500GT offers faster DDR3 memory but only 256Mb of it which is not enough. The 8600GT has an over abundance of memory, about twice what you need, but it is slower DDR2.
Echoing the above posters, you should defiantly look into a 4670 512Mb card.
It is a MUCH better performer, about twice as fast, and will not cost much more.
That 8600GT with 1GB of memory is an underhanded marketing ploy by Palit. It's like sticking a huge whale-tail spoiler and nice rims on an old POS Civic and calling it fast, but it's still a piece of poo.
Definitely go with the 4670 as recommended. Or if you want to stick with Nvidia, the 9600GSO can be had in the same range after rebate.