VR Zone published a list of the Radeon HD 3800 series' features. Apparantly there will be a Radeon HD 3870 (RV670XT) and a Radeon HD 3850 (RV670PRO) card.
The Radeon HD 3850 will be clocked at 700MHz with 1800MHz memory while the Radeon HD 3870 will feature a 825MHz GPU and 2400MHz memory. Both cards are made on a 55nm process and support PCI Express 2.0, DirectX 10.1 and UVD.
Superscalar unified shader architecture
320 stream processing units
256-bit memory interface
Shader Model 4.1
PCI Express 2.0
ATI CrossFireX multi-GPU support. Up to four cards with AMD 790FX based motherboards.