By far the best one I've seen so far is the I-Mate Momento. My godmother gave us one for the wedding, and I like it a lot. The resolution makes the photos look great. You can set it up to track any RSS feed, though I'm still working on getting it to work with an Apple Airport Extreme (it seems to have some issues with the wireless security that Apple incorporates).

If you just use the frame with an SD card like we are, it works perfectly fine. It's also very easy to use and has a nifty RF remote that stores in the back of the unit.

The main issue with the frame is the styling. Your parents might not like the modern styling, but it looks pretty good in our place. Plus the build quality is far better than I've seen from your average display unit in Best Buy.