Math problem of the week!

After reading a blog entry today about interactive math journals (see Runde's Room) I ran across an introduction to this amazing math problem website!  Waterloo Mathematics is the site.  This site provides a problem of the week for grades 5 thru 12th grade.  It is free to sign up and the questions are emailed to you each week.  You can also go back in the archive for previous questions.  Each question is aligned with math strands and has curriculum  resources to go with it!