The guys from FUD Zilla wrote an article with all the specifications about the upcoming graphics cards from AMD.
Here's a quick summarized version:
Radeon HD 2900XT: 742MHz core, 1650MHz memory, 512-bit memory bus, 512MB memory, 32 shader units and 16x2 ROPs. It has 700 million transistors and will cost 399EUR/$399
Raedon HD 2600XT: Paper-launch on May 14th. 65nm, 800MHz core, 2300MHz memory, 120 shader units, 4x2ROPs, 390 million transistors, 128-bit memory, 256MB memory. Will be priced at 199EUR/$199. The Pro version will arrive later.
Radeon HD 2400XT: Paper-launch on May 14th. 700MHz core, 1600MHz memory, 40 shader units, 4x2ROPs, 180 million transistors, 65nm, 64-bit memory interface, 256MB memory. Will cost about 99EUR/$99