In a press release issued today, AMD has announced the next addition to their Radeon HD series, the ATI Radeon HD 2900 Pro. The new unit is already available for retail, and comes in several variants.
It will not feature a 256MB memory capacity like many cards are today. Instead, it'll be available as a 512MB or 1GB part. Each version will be functionally identical, but the 1GB variants will have an option for a larger heatsink, probably to help keep the larger amount of RAM cool.
You can read the full press release in the comments section.