I have got 9" and 7" Philips frames. When I got them a few months ago, the Philips frames were the only ones that I liked the IQ on. They were quite expensive compared to some other brands, but worth the difference.
Perhaps some other brands have come out with better frames in the last few months.
I paid about £80 for my 7" Philips (normally about £120), but the 9" was quite a lot more.
The two (7" or 10") i-mate momento frames are very good. They use the philips LCD so get good picture quality. My favorite feature of them is the built in wireless. Your photos can be shown from card/usb stick etc or you can use WMP11 library sharing and stream them directly from the PC. I find this ideal as you just add new photos into your library and they show on the frame straight away. It also has compatibility for Vista sideshow allowing it popup a message when you have a new email etc although I havent tried this yet. Only thing I dont like is the menu interface can be quite slow and getting it onto your wireless network can be a bit of a nightmare