Correction, practically every card you can get at a retailer will run source games properly. I have a ati hd2400 pro, it's so slow it isn't even sold anymore. Outside OEMs of course, which is how I got it (temporarily, didn't want to spend that much money all at the same time). Nevertheless, all Orange Box titles run quite smoothly in higher resolutions with all details on, so the card should do the trick wich cs, too.
If you're looking for something that will run the more recent breed properly (and if you have enough RAM and CPU to make it really pay off), check any of the GeForce 9800GT cards out on the market. They go for little more than 100 ? around here.