DailyTech has some information on ATI Radeon HD 2600 and 2400 boards. Two Radeon HD 2600 flavors, Pro and XT. Partners will have many variations of the 2600. They will include GDDR4, GDDR3, and DDR2 in 512MB and 256MB. Radeon HD 2400 will have 256MB and 128MB of memory.
The 2600 and 2400 cards will be much cheaper than the 2900 cards and they all will feature DirectX10 support.
Find out more here.