Finding Missing Number in a Series http://www.funbrain.com/cracker/index.html Puzzle Playground http://www.puzzles.com/PuzzlePlayground/WelcomeToPuzzlePlayground.htm Play with Numbers and Give Your Brain a Workout http://www.mathplayground.com/wordproblems.html Houghton Mifflin/Education Place - Brain Teasers (Archived list - changes every few weeks) http://www.eduplace.com/math/brain/arch/index.html Checklist for Problem-Solving Guide - .pdf format http://www.teachervision.com/tv/printables/cc/ma1-pscheckguide.pdf