Thanks for your continuing input, Polly.
I think the PRS300 is a no-no for me. I think I'd prefer a 6" screen and I would prefer a SD card slot too.
I like the 505, but as you say it's discontinued. And the 600 looks nice, but I've read a lot about the screen reflection, and I don't know if a touch screen is for me.
I like the Iriver story, but I've posted in the relevant thread for that, because it seems people have had problems.
I'd prefer to spend about £200, and buy it from a store rather than online in case of any problems.
This is a hard decision!