The reviews show also a keyboard accessory (see photo) for the BestPro DMP-1. This multifunctional device is really pretty impressive.
Reviews are on MPNavi (Korean) and on KBench (Korean). Like always Korean reviews feature tons of photos, so it is worth to take a look at them.
More details also on DAPReview.
Another interesting PMP featuring similar functionality is the Centrix MVP-100.