Andrew Stadel has created an amazing website called www.estimation180.com. I use this with my students every day. If you aren't already using it with your students, I encourage you to do so!
Because I am at a 1:1 school, I created this template for my students to complete. I took what Mr. Stadel has on his website and adapted it for my personal use. Feel free to use mine, adapt mine for your own personal use, or check out what Mr. Stadel has on his website.