I have a prejudice against sheet music, as I don't read worth crap -- weirdly though, I enjoy sheet music for JS Bach & Debussy.
If you're thinking of getting loose from the I-IV-V shuffle, the best thing you can do is
listen. I have a few players I'll obsess on, repeating songs or entire albums, before I go & woodshed for an hour or two. While I'm nowhere as good as ANY of 'em, it breaks me out of the comfortable ruts.
Rather than any book, go & pillage YouTube. A fair bit of Robben Ford. Here's a simple bluesy one to get you started:
http://www.youtube.com/watch?v=...GjI4&feature=relatedAlso look for the keyword
pentatonic.