ehh.. there's a reason these went extinct a while ago =/
last i heard, red book was the big portable e-book makers. they sold out to gemstar or something, and i haven't heard of them since. a quick search showed that the reb 1100 model seems to be their flagship that was based off the old red book. couple of these available on ebay.
their inflexibility was a huge downfall, i think they were really hoping to stick to only certain formats in order to corner the market. instead, they ended up shooting themselves in the leg. at least this was my understanding.
on the more portable side, PDAs such as the compaq iPaqs are beocming much more powerful and versatile. basically a mini-pc, they allow you to read pdfs, docs, etc. on the road as well as almost the full functionality of a laptop/desktop.
tablet pc's are the next size up. full laptop capability but portable enough you can just bust out and read.
as for inbetween, it just doesn't really make sense, so you're going to find a hell of a time finding a dedicated ebook reader. you're looking for something that's bigger than a PDA with LESS functionality. or smaller than a tablet PC and STILL less functionality. my advice, go with a large screen pda
if you haven't seen the new screens on these suckers... well now's a good time to shop