Eurogamer (linked above) posted news that a PSP-4000 will be released in 2009, which will apparently feature slight hardware upgrades.
They also mentioned that a PSP2 is still planned, despite David Reeve's recent denial.
To quote: Sony plans to refresh the PlayStation Portable product line with a PSP-4000 model in late 2009 and launch a true successor - a PSP2, if you like - later.
Publishing sources, speaking to Eurogamer, were unable to provide any further detail on next year's update, which will presumably follow this year's PSP-3000 in taking an iterative approach. The PSP-3000 launched this October and followed a 2000-series model, the first Slim & Lite, in September 2007.
Even fewer details were available on the PSP successor, but we're told that developers are already working on games.
Sony has not ruled out either scenario, despite SCEE president David Reeves' assertion in MCV last week that "there are currently no plans for a PSP2". "I go to Tokyo quite a lot and no one has referred to it - I think they have their hands full at the moment," he said, non-committally. More PlayStation 3 News...