Anthologize is a free, open-source, WordPress-based platform for publishing. Grab posts from your WordPress blog, pull in feeds from external sites, or create new content directly in Anthologize. Then outline, order, and edit your work, crafting it into a coherent volume for export in several formats, including PDF, EPUB, and TEI.
Another key item for creating books for distribution via online merchants -- Kindle, nook, kobo, scribd, etc is support for cover art for all formats.