You also didn't mention any kind of budget. How much are you willing to spend? If you just want the best available Nvidia GPU currently available then that's the GTX 295. I doubt you're looking to spend $500 on a GPU, though. Where do you live? Without knowing that either, I'll just use Newegg.
GTX 275 boards offer pretty good price/performance.XFX GX275XAHFF GeForce GTX 275