The iPhone and recently-released iTouch are gathering a bit of attention as an eBook platform.
As this article from Tim O'Reilly points out, Apple already has quite an effective distribution platform in the form of iTunes, and there's speculation about Apple extending its reach to encompass eBooks, and publishers HarperCollins have even launched an eBook service tailored for the iPhone.
The iPhone and iTouch have pretty good resolution displays (about 160ppi — twice that of a PC screen), and the actual user interface is getting lots of praise for its ability to deal with presenting web-based content on a small device — have a look at the guided tour video of the iTouch from the Apple site.
There are a number of custom-made solutions out there already including one being developed on the Google code site, though often they're a little bit fiddly to install and use.
Given the iPhone / iTouch's use of a fully-fledged browser (Safari), it may be that the eventual mechanism for reading eBooks on these devices will be browser-based. Although you can use Safari on the iPhone / iTouch to read PDFs and HTML pages, the current obstacle to eBook reading is the fact the the browser only works well when in a place of WiFi reception — there's not a good mechanism of cached or offline browsing (though Apple's in bed with Google, and Google Gears would do the trick). Again, so people have been busy trying to find ways to overcome this hurdle, including the use of the mostly forgotten data URL standard.
At the moment, the iPhone / iTouch is not quite there for eBook reading, largely due to the problem of easily accessing content offline but it wouldn't take too much for Apple (or a capable hacker) to solve this.