There are some awful ones so be careful
You need to first decide on the screen size (diagonal 8 inches etc..).
Then look for the screen resolution.figures.
An 8 inch screen at 800x600 loooks fairly good. Anything less looks a bit disappointing in my opinion.
None of them seem nearly as good as a PC monitor.
Sound quality is generally awful but that is not too important.
Imagin 8" Aluminium (with Blue LED Surround) Multi Media Digital Frame from Cameras2U.com at �89.99 seemed OK and I bougfht one as a present.