Sites that I can't do without as a math teacher (and what's so special about each one!) Links to virtual manipulatives, discovery-based lessons, free graphing software, question prompts, eBooks, and more.... Tons of resources for math teachers
Enriching Math is a problem-solving and probability game for middle-school and early high-school students. Print out the grid or draw it on paper, find twelve counters and two ordinary dice, and from the rolling of the dice, see which counter reaches the end of its row first.
Slope Hot Seat Game - Students sit in lines of 4. Last person in each line gets cards with pos, neg, zero, undefined written on them. Teacher posts an equation on the board. The last person in the line chooses the kind of slope & passes that card to the person in front of them. The student looks at the answer and if they agree, they pass it up. If they disagree, they pass it back. When the 1st person in the line gets and agrees with the answer, they hold it up.
It wouldn't let me pin the main page, but this website is a collection of math questions called Stella's Stumpers. The questions (over 600!) are sorted by math class, and they look to be a great resource for bellwork.