The Daily Bite provides a large set of warm up problems already printed on transparencies.
It is not clear to me that the problems are ideal for warm ups. However, they all appear to be appropriate for the grade levels advertised, and they strongly mimic the format of our standardized assessments. Using these regularly could be a great help in getting our students to overcome their test anxiety.
A notable advance is that, in addition to preprinted transparencies, the questions are now also all available as powerpoint slides, for use with projectors. Send email to the website's contact address for more information.