ATI's Radeon HD 2600 XT and PRO will both have a 128 bit memory interface. They are after Nvidia's G84 now known as Geforce 8600 GTS and GT. The good thing is that Nvidia still uses 128 bit memory interface for this $150 do $200 market including 8600 GTS and GT.
ATI's RV610LE the card that should consume less than 25W and is very popular among the system integrators and the OEMs has 64 bits only. There is no reason to panic as Geforce 8300 GS has the same memory interface but needs more power.
ATI tried to keep this fact from the public eye for a while but what can you do if you want DirectX 10 below $70 with Shader model 4.0 and some cool video processing you will have to live with 64 bit memory. It saves AMD a few bucks per card as the Build of Material popularly known as BOM is smaller for the 64 bit memory card.
Yeah, basically DAAMIT screws your card and cripples it from 128 bit memory to 64 bit just to earn 2 to $3 more. It is called capitalism and most of us live in it.