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There are a few sources of DRM-free publications, including Baen Books (science fiction and fantasy), which even has a Baen Free Library to seduce you to further output by the same authors -- especially for long series. They even furnish a free CD for a few of their hard covers. They have found this to be very profitable for future sales. There is also Project Gutenberg (about 40,000 articles and novels, mostly old and free of copyright). All of these are available in most of the major e-reader formats. And bravo for Calibre!