I recently subscribed to “Reader Plates” for the iPad (http://readerplates.com/iPad) so far, I like it very much.  The cost is $9.99 per month and all the data can be downloaded directly to your iPad using WiFi.

>>>  Their Web site states:

At this time Reader Plates are available only for the Sony PRS-505, PRS-900, PRS-950, and the Amazon Kindle DX electronic book readers. <<<