I found the O'Reilly book on Fedora very useful, even though I've been using the distro for several years, so check out their
Ubuntu hacks, by Oxer
Ubuntu Linux for non-geeks, by Grant
One of the classics is their
Running Linux, by Walsh
although, like a lot of Linux books, it aimed rather more at the system administrator than the home user. A lot of people seem to thing it cooler to use complex command-line instructions or to edit scripts than to use the perfectly good software utilities that come with the distro ...
Don't neglect Amazon: their customer reviews can save you wasting money.