I am currently trying to find a good series of maths tasks that I can give to my upper maths students to really challenge them at home and am not really having a great deal of luck. I did however come across a great site here that has some extension activities correlated to everyday maths curriculum.
Hold the Phone I just found 2 more good ones
And here are 2 more additions
I would love to hear of any that you know of and will definitely share them here.