The New Tunisian Crochet: Contemporary Designs from Time-Honored Traditions by Dora Ohrenstein seems to be the most thorough book I've ever seen on Tunisian crochet. Most of the ones I've seen have the basic instructions plus how to work various special stitches.
This book includes double-ended hooks as well as combining Tunisian crochet stitches with regular crochet stitches. The patterns look interesting and the combination stitches make the work more interesting.
Check it out if you have any interest in Tunisian crochet or its variants.