NW-A800 series of Walkman devices. Our tipster tells us to expect a launch in September so we'll know the poop soon enough.
Update: A bit more rumor mongering for ya. The NWZ-A series will launch in 2, 4, and 8GB models in black, white, silver, and pink (8GB is black-only). The NWZ-S series includes an FM tuner. Both support USB Mass Storage with an announcement as early as Friday.
[Thanks, Anna and Dan]