If you want CUDA, then of course Nvidia is the one you need. In that price range, you could go for an upper tier GTX460 1gb. I recommend the MSI Hawk Talon Attack edition, the Gigabyte Superoverclock, or the ECS Black.
For a little more, you can bump up the CUDA processing power and stay within your price range with a GTX470. Again, I would recommend the MSI or Gigabyte with custom cooling. EVGA or Asus are also solid choices.