In his 1961 book Return from the Stars, Polish writer Stanislaw Lem wrote about what he called a lecton;

The bookstore resembled, instead, an electronic laboratory. The books were crystals with recorded contents. They can be read the aid of an opton, which was similar to a book but had only one page between the covers. At a touch, successive pages of the text appeared on it.

But optons were little used, the sales-robot told me. The public preferred lectons - lectons read out loud, they could be set to any voice, tempo, and modulation. Only scientific publications having a very limited distribution were still printed, on a plastic imitation paper.
(Read more about the lecton)

In this short passage, Lem provides a very accurate description of both electronic books and e-book readers almost fifty years ago. Not a bad prediction!

In his 1959 short story War Game, Philip K. Dick wrote about an office memo that will read itself to you;

"Good morning," the first memo said in its tinny, chattery voice, as Wiseman ran his thumb along the line of pasted tape.
(Read more about the memo-voice)

In his 1941 novel Methuselah's Children, science fiction Grandmaster Robert Heinlein wrote about what he called a newsbox (also called a news-receptor);

[He] was bending over the news-receptor, his eyes pressed against the microfilm viewer.

Lazarus punched the keys. The machine chattered and whined as it scanned and rejected track sped through it, then the film slowed with a triumphant click. "The DAILY DATA," it announced. "The only midwest news service subscribing to every major grid and private photophone to Luna City...
(Read more about the newsbox)

In his 1934 novella The Lost Language, writer David H. Keller wrote about what he called a sound-transposing machine;

"I have done it," he said simply, "and you do not owe me a cent... In a month's time, tired people will be placing pages of a book in their machine and hear it read to them..."
(Read more about the sound-transposing machine)

Incredibly, the idea that a machine could read a book or a newspaper to you is more than a century old. In his 1899 story When the Sleeper Wakes, H.G. Wells wrote about what he called a babble machine;

When I was a boy - I'm that old -- I used to read printed books. You'd hardly think it. Likely you've seen none -- they rot and dust so -- and the Sanitary Company burns them to make ashlarite. But they were convenient in their dirty way. Oh I learnt a lot. These new-fangled Babble Machines -- they don't seem new-fangled to you, eh? -- they're easy to hear, easy to forget...

Asano touched his arm and gave him a warning look, and forthwith another of these mechanisms screamed deafeningly and gave tongue in a shrill voice. "Yahaha, Yahah, Yap! Hear a live paper yelp! Live paper. Yaha! Shocking outrage in Paris. Yahahah! The Parisians exasperated by the black police to the pitch of assassination. Dreadful reprisals. Savage times come again.

...in all the more comfortable private apartments of the city were fixed Babble Machines that would speak directly when a lever was pulled. The tenant of the apartment could connect this with the cables of any of the great News Syndicates that he preferred.
(Read more about the babble machine)

If you can think of additional (or better/earlier) examples, I do enjoy collecting them...

Update 25-Feb-2009: I forgot this excellent example from Douglas Adam's Hitchhiker's Guide to the Galaxy; the Hitchhiker's Guide is described as an electronic book:

Ford pressed a large red button at the bottom of the screen and words began to undulate across it. At the same time, the book began to speak the entry as well in a still quiet measured voice. This is what the book said...

End update.