http://www.argos.co.uk/static/Produc...er/5011283.htm
Nook Simple Touch Glowlight £49.99 in the UK
Meets all requirements in original post, although does have a touch screen.
I've recently upgraded from a PRS-505 I've had from new since 2007 and, having tested quite a few, found this to be the current best mix of functionality vs form available. Yes, the Nook store isn't the best, but if most titles are to be sideloaded, then there's no problem.