Here are links to the resources that Charlie mentioned at the workshop, including the ppt slides:
Dicey Operations
Forwards Add Backwards
Cryptarithms
Image
Kangaroo Subtraction
Dozens
Factors and Multiples Game
Gabriel's Problem
Product Sudoku
Summing Consecutive Numbers
What's it Worth?
Take Three from Five
Cyclic Quadrilaterals
M, M and M
Unequal Averages
Wipeout
Route to Infinity