Two ... but it depends on how you count. I've got the JetBook Lite and I do almost all of my ereading on it. When prices dropped after it was discontinued I picked up a second as a spare -- but it's still in the box.
I also have a Pandigital Novel. The Internet Archive has a large number of old issues of Galaxy Science Fiction from the late fifties and early sixties, and the PDFs are pretty good. In general, the PDN does a better job with PDFs than the Jetbook, but in the case of Galaxy (and other digest sized magazines) it really shines.