I am the author of three logic and critical thinking books, which are published by Classical Academic Press:
Discovery of Deduction (co-author)
You can find these books at Classical Academic Press here.
And you can also order them from Amazon:
Everyday Debate (I recommend starting with this one.)
You can read more about the importance of critical thinking here:
I also recently published an article on playfulness with Tiny Buddha, which you can read here:
And here is a recent article I wrote for Tiny Buddha on Mindfulness: