1UP suggests that Microsoft may have lowered existing 360 shipments in an effort to flush out old inventory in favor of newly enhanced hardware; like consoles with HDMI support and a larger hard drive. Game Informer was a lot more specific in saying: "Retailers have confirmed that the new SKU is in their systems, set for a May 1 release for $479.99. In addition to the new [HDMI] interface, the system would also pack a 120 GB hard drive into its nifty black exterior."
Keep in mind this is all conjecture, however, as Microsoft's Shane Kim told 1UP last week that the company has "nothing to announce at this time" regarding new SKUs. Still, the grapevine implies that something's brewing over at Microsoft's Xbox division.