What about the Franklin Ebookman? I used to use one of them and it was strictly for reading ebooks or at least there weren't many apps available for it that I could find. Mobipocket stopped supporting it and books past a certain point therefore couldn't be read on it but it existed long before the Kindle. Of course it use a different display and was a battery hog (4hrs charge tops) but it was a dedicated ebook reader. (1999-2002)
http://en.wikipedia.org/wiki/Franklin_eBookMan