I like the Sony PRS-350 because it is small and neat (but of course, smaller screen).
I got my wife one and preferred it to my own Bookeen Opus (which had awkward buttons and crashed too often), so got myself a Sony too.
They were £30 and £23 inc postage on eBay.
I avoided the Kindle because of its locked down nature; in particular that you can't borrow library books in the UK with it.
Downsides:
You need to install Sony Reader to get the driver that is needed to use them with ADE, even if you don't want to run Sony Reader.
Won't work with ADE2.0 and Overdrive library books; however, ADE 1.7.2 seems a lot more stable than ADE2.0 and they work fine with that.
