I am not a huge fan of coloring or workbooks, but they do seem to appeal to children. Luckily there are some beautifully designed ones out there to please us both!
Kumon's workbooks are without a doubt the best as far as design and quality. I love the philosophy and skills the books develop and the fact that the beginner sets really encourage parent/child interaction.
These coloring books from rock scissors paper are sophisticated enough for me to want to pull out the crayons.
I like the unusual subject matter of these coloring books available at Budget Art Kids.
Many museum shops carry the Modern Patterns series by Mindware.