The Toxic Radeon HD 6950 is a very good choice, if you can find it. Possibly the fastest 6950 in the market. And it's built for overclocking, with a dual bios allowing easy unlock to 6970.
Just checked ncix quickly, there are a lot of 6950's with good rebates. 229 dollars is a smoking deal. The toxic is a very hard find at the moment, and I hear they have a noisy cooler.