I have found a great E-Book reader for the Blackberry. It's called Mobi Pocket Reader, and its free. It's available for a lot of other phones too. You can download books "over the air" or you can copy them to your Blackberry using the desktop manager software - MobiBooks looks in the Ebooks folder (although this can be changed via the options menu).
I have been enjoying some of the many E-Books available as free downloads in Mobi format from ManyBooks.Net. If you're not a fan of classics, there are also a lot of commercially available books in the built-in libraries.
Creating and Converting Books
It doesn't stop there though. There is free MobiPocket Creator Home Edition software available for creating MobiReader books from a variety of other formats, including, text,html, pdf and doc.
This means that the entire resources of Project Gutenberg are open to you as well as a lot of online fan-fiction and business documents, whitepapers etc.
Creating Your Own Books
Best of all, there is the ability to create your own books for free. MobiBook Creator provides a bunch of handy templates for recipe guides, shopping lists and other databases but I personally feel that the best options are centered around the conversion of existing business documents.
At first, this may not sound terribly exciting but think how handy it would be to have your Disaster Recovery and/or Business Continuity plans on your Blackberry as an E-book.
I'm sure that everyone has other documents like IT Strategies, lists of IP and Mac addresses, WAP codes and Serial Numbers for your Software inventory etc, which rarely change and could benefit from greater offline availability.
Setting these things up as Ebooks could be just the ticket.