Previewed at WWDC, launching in the fall.
Evidence for New MacBook Pros [Updated]
The current MacBook Pros which were released in June carry a system identifier label of "MacBookPro3,1". One reader notes that an application called MiniBatteryLogger provides public battery tracking logs, and recently revealed an entry with an identifier of "MacBookPro4,1". "MacBookPro4,1" is presumably the identifier for the unreleased MacBook Pro revisions. The author of the application states that the identifier is obtained automatically from the system, though there are no guarantees that it wasn't faked.
However, this same new "MacBookPro4,1" identifier has also been found in the latest developer seeds of Mac OS X 10.5.2 from Apple. In contrast, the public version of Mac OS X 10.5.1 does not contain the "4,1" identifier.
In many ways, all this does is verify what we have presumed to be true... that MacBook Pro revisions are coming, and soon enough that the Mac OS X 10.5.2 will support them, but it's still somewhat reassuring for those waiting patiently for the new MacBook Pros.
Update: We've received confirmation that the battery log information came from an Apple IP address, so it is believed to be authentic.