Apparently Max Console has known about these for awhile and now that retailers are letting the cat out of the bag, it's OK to talk about it. The Datel 4 gig hard drive is en route. It includes a battery that is expected to double the playing life of your PSP and double the storage (we've just started to see 2 gig memory sticks).

Datel 4 GB Hard Drive Confirmed [Max Console]
Pre Order the Datel HD here