I would go with the 9600xt. First, the 9600xt does not require you to plug your Power Supply directly into the video card because the 9600xt core is 0.13 technology. And, the 9500 Pro would probably only give you a few more FPS in games than the 9600xt, nothing noticable in regular game play.
Most important to note, a retail version of the 9600xt, either built by ATI or another manufacturer, comes with a coupon for a free full version of HL2.
But remeber that the 9600xt OEM version do not come with the coupon. I believe newegg is selling a Retail version of the ATI 9600xt for $189. So it is IMO that the 9600xt is the way to go. You wont be disapointed.