Like Stung, I've mostly downloaded free pages but I recently grabbed a book of mandalas at AC Moore for about $5 for my mom. I'm using my 50-pk of colored pencils, I'll only use crayola brand, I'm a snob that way.
You could also download the free ones & create your own book, that way you could pick & choose what you like the best. With some patterns that I really liked, I printed a few copies so that I could do them in a variety of colors.