How often do you find yourself asking, "isn't there another way I can demonstrate a particular math topic to my students because they aren't understanding what I've been doing thus far"?
Try finding a suggestion at K-5 Math Teaching Resources.
This website has loads of ideas to peruse through. You can filter your search by grade level, strand, Mental Math Concepts, Interactive Whiteboard ideas, or Centers.
When looking into a grade level of activities, ideas are separated by standard, with links to printables if necessary.
The links to Interactive Whiteboard Resources take you directly to the IWB activity that relates to the concept.
There are many activities ready to use in a centers based environment, providing you have or create the manipulative for the activity (note, they do provide links to download these interatives). For example these are a few of many ten frame and dot card activities you can use in a number sense center.
There are many Mental Math Activities available, including a nice overview of using empty number lines in your classroom. And don't forget to check out the ideas for your 100th day of school.
This website has been a golden goto resource for k-5 math ideas and activities for several area teachers. Aren't we all looking for additional ideas?