Going down the line from the links you posted:
Ceiva - http://www.ceiva.com/home/hp/index.jsp
- didnt really provide a lot of information, and it seems there is a fee for their service. Also doesnt appear to let you use local photos.
iGala - http://www.thinkgeek.com/electronics/digital-photo-frames/b425/
- looks cool, appears to be free of any monthly service fees, however it didnt appear that you could use local (as in on your lan) photos..they mention rss and different sharing sites. Im pretty sure it could be configured to work with local stuff, but I wouldnt count on it as it would require contacting the manufacturer more than likely.
D-Link - http://www.dlink.com/dsm-210
- This one appears to be more of an out of the box situation as it supports upnp and linuxMCE has a upnp server.
PhotoVU - http://www.photovu.com/digital-frames/overview.php
- This one gave me a sleazy feeling, but it appears to support displaying photos over you local network and is the only one of the links i followed that mentioned linux setup instructions. they charge for software updates though...
Anyways, hopefully you sensed my theme when checking these out.
no monthly fees (how they managed to figure out a way to charge for that is a tribute to capitalism) and can share files over the local network ,so that linuxMCE can make use of existing functionality to allow the device to be set up simply.
Hope that helps