Tweaktown reported http://www.tweaktown.com/news/7593/index.html that 1024 MB GDDR4 Radeon HD 2900 XT is just around the corner, shortly after that Coolaler.com forum member showed few pictures of it.
The card is the same size as 512MB version, 9-inch card. It has 16 memory chips, eight on the front and eight on the back, Samsung memory chips that are rated at 0.9ns, which should theoretically give 1,111MHz. The "guess2098" Coolaler.com forum member managed to overclock it from default 743MHz to 858MHz for the core and from 1000MHz to 1153MHz for memory.
Some 3DMark results are posted, and the system used is "Core 2 Extreme Kenstfield Q6850 at 4GHz, Asus P5K-D, GSKILL 2GBHZ at 1000 CL4, TT 1200W PSU, TR 120-X".
You can check out the bigger pictures over at http://www.coolaler.com/forum/showthread.php?t=154586