$214 Radeon 9800 Pro if you must buy now. It's a very fast and reasonably future-proof card at a reasonable price.
Your 4800 is still pretty decent for most games as long as you forego AA and AF. I'd wait until mid-March to see how the introduction of nVidia's and ATi's next generation (NV40/R420)--both claimed to be 2-3x faster than their current high end parts (5900/9800)--shakes up the pricing landscape. Still, I doubt you'll see 9800 Pro's or 5900's for much less than they're selling for now, and you won't be able to buy a next-gen high-end card for less than ~$400 at launch (mid-April), so you may as well buy the 9800P now and enjoy it.