Oh here's a can of worms!
Looking for a digital photo frame was a pure nightmare Mike, absolute nightmare. It chewed up hours and hours of my time.
I was looking for something to show digital pictures. I ended up with the Zen Vision W instead of a photo frame (portability, battery life, and lots of other reasons). The Zen W has a screen res of 480 x 272 and output to TV at something much higher than that. That bare minimum res of 480 x 272 was the same or higher than ALL but the very best few 7" frames I found.
I then went looking a second time a few months after that for a product to fit the same requirements, for my mother at my dad's request. He wasn't happy with the 4.3" screen size of the Zen W. I ended up buying one from "Digital Frames Australia" but I can't find their site right now, will find the bookmark at home tonight and post it. It's bluetooth and everything else under the sun capable, and 640 x 480.
The options out there are endless. Really. Really really endless. Unfortunately though none of them except the Philips have a battery (50min life), and very very few of them have good screen quality. Also, I found most of the ones advertised on eBay in particular incorrectly advertised their screen resolution (quick cross checking and then email to the store owner always turned this up).
As for the one I bought for my dad to give my mum, I feel it's not a good solution for the task. It has not battery, which I think is not worth the extra screen size. It is more clunky to use than the Zen, barely a scratch of the internal storage, worse viewing angle on the display, and many more reasons. But he prefers it because of the larger screen size.
If I were buying a frame I think the Philips one is the best, it had a res of 700something x 400something at a 7" size, and 50min battery, and was not too big physically. But it costs a bit from memory.
I viewed several 7" ones in real life before buying and all of them had very suspect screen quality, sure the images were OK, but put it next to a laptop and you gasp at the difference. To get better screen quality you need to research pretty heavily to find the high res, good viewable angle ones with good contrast, and be prepared for about $200 for 7" or $400 for 8" - 10".
That's my memory of it all.
I had about 50 bookmarked at the time I was looking for one, there are that many re-branded versions of the same, or variations on the crap ones, etc, etc.
Good luck
PS, if you want it for a digital photo album to take around the place, there are a few options like the Zen W I could elaborate on. Some really really cool ones
