if you want to get a quick picture of how wide and varied the eBook market is, visit the UK Book Depository and choose to customise your preferred reader for eBooks. It gives you a great list of devices to choose from:
It’s a wide market!
The iPad is highlighted above as I was looking for books for it. And interestingly, even though it supports the ePUB standard (and they recognise it does on the site) they say they’ve no books. DRM strikes (itself in the foot) again!