I've had my eye on the first one for several months: The Children's Mathematics Calendar 2011.
The math calendar contains a new problem each day. Although I haven't seen the 2011 calendar, I own an older one and enjoy the format. According to the Amazon product description, "This calendar includes stories that make math ideas come to life, problems with new twists, and ways to share math exercises with parents and friends. Much more than just a reminder of the date (though it does that too), this calendar stimulates curiosity and imagination and helps children develop a positive attitude about mathematics."
If you are looking for more difficult mathematics, check The Mathematics Calendar 2011
I will be compiling a list of gift ideas on my Math Gifts and Games page, linked from the menu on the top of the homepage.