Calibre is about the best thing since sliced bread. It is able to convert basically any type of Ebook format into EPUB, which is what my Nook reads natively. It seamlessly syncs with the Nook as well, which is a huge plus, and all of this happens in Linux. I highly recommend this software. Just make sure not to queue up too many jobs, or it might DOS your computer for a bit. The PDF conversion is especially intensive. It makes quick work of short documents (hundreds of pages), but documents that are thousands of pages take much, much longer. The only capability I’m missing currently is conversion of DOC to EPUB, but I can use OpenOffice to convert a DOC to HTML, and then import that into Calibre and convert it, so that works.