Amazon are doing one in the states called Kindle (latest version Kindle2) which looks good. It can be purchased through Amazon. Waterstones have the two Sony things on display - you should be able to try before you buy...which helps.
I got a Kindle for Christmas. Still playing with it and finding out what it can do. I like it so far and have downloaded a few books. It takes MP3 files to you can download from your PC and listen to music while you read. You can use it for the internet but it is not really designed for this so it is limited in it's use. You can even visit RR on it.