Hi Slainte,
I think maybe my eBookwise reader is about as simple as it gets. (Inexpensive also, at $139.) It doesn't do anything other than show books in .imp format, not much in the way of graphics. I've been getting my reading material at
www.ebookwise.com, the same place where I ordered the reader device. I like getting books there, because I don't have a lot of time to be fooling around with converting formats, etc. Instead I prefer to spend my few stolen moments actually reading. The book downloads are quick. The device if VERY user friendly. If you are only interested in a device for reading, then this might be one for you to investigate.
One caution: I am having trouble with the device not reading it's smart media card. I'm waiting to hear back from eBookwise about what they will do about it.