It appears that ATI will be bringing us 512MB cards very soon. At least, they are certainly working hard to. The new cards would allow users to play Doom 3 with full quality texture settings, as John C. actually designed the game to be able to use a whole 512MB of texture RAM.
Not only will ATI have X850 cards powered with a whole 512MB of memory, it will have X800 boards with 512MB of memory. ATI already pre-announced the X850 series with more memory at Quakecon but until now, none of the partners finished their design as this memory significantly increases the price. You can expect that an extra 256MB of memory will increase the price by an additional $100 or even $200 to the already sky high price of $499 or $549.