Here are a couple of those ideas and one or two others:@fawnpnguyen: "I was brainstorming with a couple of 6th grade math teachers at another district, and we were listing out a possible warm-up/math talk schedule, something like Monday: number talk; Tuesday: visual pattern; Wednesday: estimation 180; Thursday: fun fact, or WYR, or Keeping Skills Sharp, or SBAC/review question; Friday: personal reflection.
One Hundred and One Questions - An image or video is presented and students ask any question that comes to mind. While I personally wish the prompt was "What math question comes to mind here?", it is a good place to help them develop the ability to ask questions of the world round them and to see that math isn't just a classroom activity. Browse beforehand and record the links of the ones that fit your current material or your mood.
Math Arguments 180 - The goal is to have students question their assumptions and bring those assumptions to the front of their minds for conscious consideration instead of letting them hold on to common misconceptions that mess up their thinking. Still in the development stages. The Math Concepts Challenge is also for teachers, though your students might be charged up for it.
Math Talks - Prompts for discussion with your students.
Would You Rather? - students are presented with a choice. They choose and then have to justify their choice. "Would you rather have a bag of nickels that weighs as much as you do or a stack of quarters as high as you are?"
Graphing Stories - a video is shown and the students need to create a graph of some data from it. The video contains a graph blank that shows the independent and dependent variables. Usually, these are time-series graphs of height or altitude, but if you only show the "action" portion, you can have them graph whatever quantities that come to mind.
The UVM Math Contest - Problems from the University of Vermont High School Math Contest. These are given in the spring of Pre-Calculus and are meant for mature students who have had a good algebra II background. These questions are to be solved without a calculator or technology of any kind; figuring out the method is the whole point. Attempting a whole test in the allotted two hours would challenge even the best math teachers. Scores of 15 out of 41 are considered excellent.