Mobipocket has released a free ebook Reader for Blackberry supporting .pdb files and Mobipocket ebooks. (see some screenshots below)

Convert also for free your .txt, .html, .doc, .pdf documents to Mobipocket ebooks with the free Mobipocket Desktop Reader : http://www.mobipocket.com/en/DownloadSoft/DownLoadReaderStep1.asp


Enjoy it!

Screenshots of the Mobipocket Reader for Blackberry :
(library, normal reading on a bookmarked page, and selection of a link in fullscreen mode)