Staring at the computer makes me cross-eyed

I’m not a complete WordPress ignoramus, but I’m close and would like to learn more, if only to work on catching up with a co-worker who has done some wonderful things.

I know how to find plenty of reference material online, but sometimes I need to back away from the computer and study a printed page. With that in mind, can someone suggest a good, in-depth but idiot-friendly reference book for creating a WordPress CMS? I’ve already got WordPress for Dummies; the next one I’m leaning toward picking up is “WordPress Complete” but thought I’d better ask the experts before putting down my $35.

Thanks for your time.