A book Id love to buy!
I love colouring! I could honestly say that its a form of meditation for me, it keeps me in the here and now and lets me feel like a child again (which is always nice!) Mandalas are wonderful to colour! You can give the same mandala to dozens of people and the different ways in which people go about colouring them is fascinating!
There are tons of great mandalas to print online and some good books to buy too...yay for adult colouring!!
My 40 yr old self is off to gather my pencils and paper...hurrah!
There are some nice pages to colour at the Printable coloring pages blog!
and you can watch someone else colour one at the cool 5min art site