GetHT downloads PDF files from Hinduism Today, an "award winning, Macintosh-generated, full color quarterly news magazine articulating Indian spirituality for 135,000 readers around the world." It is the only native GNU/Linux client available, has good proxy support, and allows you to only download the parts of the magazine that interest you.
getxbook is a collection of tools to download books from websites. There are tools to download from Google Books' "book preview", Amazon's "look inside the book", and Barnes and Noble's "book viewer". There is an optional GUI written in Tcl/Tk, and some shell scripts using OCR to create plain text or searchable PDFs and DjVu files from the downloaded books.