On my local library I stumbled over a really nice book called Effektivare Linux – Kom Igång Med Kommandoraden (its Swedish title), which essentially is a printed and translated version of GNU/Linux Command-Line Tools Summary. I don’t know if it’s available as a book in English, but it’s at least readable on their website since it’s licensed under GNU GPL.
I think it’s an excellent book for everybody who wants to learn how to use the command-line/terminal. Because it goes through 250 (170 in my revision from 2008) useful and common commands that will bring joy to your life. I have only read half the book so far, but I have already learn a lot of commands that may be useful in the future. I don’t think that I will remember every command mentioned in the book, but I think it’s good to at least know what is available, so can I look it up (on Internet) when I need it.